Concept: Ratio, Proportion & Partnership

CONTENTS

 

INTRODUCTION

The Concept of Ratio, Proportion and variation is very important for CUET. Basic fundamentals of this topic are extensively used in the areas like Data Interpretation, Time & Work, Time, Speed & Distance etc.

 

RATIO

Comparison of two numbers or quantities having the same units is known as a ratio. Sometimes we need to find out how many times one number (say a) is compared to another number (say b). The ratio of a to b is written as:

a : b = ab

In the ratio a : b, a is known as the antecedent and b is consequent.

For Example:

Gautam and Virendra have Rs. 56 and Rs. 14 with them respectively.

Then, we can say that Gautam has Rs. 42 more than Virendra or alternatively Gautam has 4 times as much money as Virendra. The latter way of comparing is by finding ratios between the amount with them

Amount with GautamAmount with Virendra = 5614=41

 

Remember:
  • Ratio is used to compare similar type of numbers (i.e. their units should be same).
  • Ratio is generally expressed in simplest form (i.e. by cancelling out any common factor between the numbers).
  • Ratio does not have any unit.
  • The order of terms is important, i.e. a : b is not same as b : a.

Example : Calculate the ratio of 15 and 25?

Solution:
Required ratio is 1525.

This can further be simplified by eliminating the common factor from both the numbers. Here, the common factor is 5.

Hence, the simplified ratio = 35


Example : 7 is what part of 8?

Solution:
Required part is the ratio of 7 and 8.

∴ part = 78.

It means 7 is 78th of 8.


Example : 348 is what part of 112?

Solution:
Required part is the ratio of 348 and 112

∴ part = 348112=348×121=34 part.

It means 348 is 34th of 112.


Example:
In a ratio which is equal to 3 : 7, if the antecedent is 33, what is the consequent?

Solution:
37=33x

⇒ x = 77


Example:
Find a fraction which bears the same ratio to 37 that 15 does to 715?

Solution:
Let the number be x

Then, x ∶ 3/7 = 1/5 ∶ 7/15

x37=15715

⇒ x×715=15×37

⇒ x=15×37×157 = 949

Let’s take the ratio of amount of money with Gautam and Virendra again.

Amount with GautamAmount with Virendra = 5614=41

This can also be interpreted in the following manner: For every Rs. 4 that Gautam has, Virendra has Rs. 1. Therefore, out of total Rs. 5, Gautam has Rs. 4 and Virendra has Rs. 1, i.e. Gautam has 45th of the total and Virendra has 15th of the total.

Hence, if the ratio of two numbers is a : b, it means for every ‘a’ parts of the first numbers there are ‘b’ parts of the second number.


Example : Divide Rs. 72 in the ratio 4 : 5.

Solution:
There are total 4 + 5 = 9 parts out of which first part has 4 parts which the other has 5 parts.

First part = First ratio termSum of ratio terms × Total amount = 44+5×72 = Rs. 32

and, second part = Second ratio termSum of ratio terms × Total amount = 54+5×72 = Rs. 40

As mentioned earlier, ratio is expressed in simplest form. Hence, if the ratio of two numbers is a : b, the numbers need not be exactly ‘a’ and ‘b’. The numbers would be a × x and b × x, where x is the common factor which would’ve been eliminated while simplifying the ratio.


Example : Amit and Atul have money in the ratio of 3 : 5. What is the amount with them respectively.

Solution:
Here, we know the ratio of the amounts with them i.e. 3 : 5.

Hence, the amount with Amit = 3x 

and the amount with Atul = 5x.

Now, there is no additional information given to calculate the value of x. Hence, we cannot determine the amount with each of them.

Hence, the answer cannot be determined.

Alternately,

Amount with Amit = 38th of the total amount.

Since we do not know the total amount, we cannot figure out the exact value of the amount with Amit.


Example : Amit and Atul have money in the ratio of 3 : 5. The total amount with them is Rs. 160. What is the amount with them respectively.

Solution:
Here, we know the ratio of the amounts with them i.e. 3 : 5.

Hence, the amount with Amit = 3x 

and the amount with Atul = 5x.

Now, we know the total amount with them is Rs. 160.

Hence, 3x + 5x = 160

⇒ x = 20

Now, we can calculate the amounts with each of them.

Amount with Amit = 3x = 60.

Amount with Atul = 5x = 100.

Alternately,

Amount with Amit = 38th of the total amount =38 × 160 = 60

Amount with Atul = 58th of the total amount =58 × 160 = 100

 

IMPORTANT RESULTS
  • The value of a ratio remains unchanged if each one of its terms is multiplied or divided by a same non-zero number.

i.e.     a : b ⇔ ab=mamb
and    a : b ⇔ ab=ambm
whatever m may be except zero.

  • a2 ∶ b2 is called duplicate ratio of a : b.

  • a: b3 is called triplicate ratio of a : b.

  • √a ∶ √b is called sub-duplicate ratio of a : b.

  • ∛a ∶ ∛b is called sub-triplicate ratio of a : b.

  • If a : b and c : d are two ratios, then product of ratios i.e. ac : bd is called the compound ratio.

  • If a : b : c = x : y : z ⇒ ax=by=cz

  • In a ratio of greater inequality, if the same number is added to both numerator and denominator, the ratio decreases, i.e. If a > b then, a+xb+x<ab 

  • In a ratio of lesser inequality, if the same number is added to both numerator and denominator, the ratio increases, i.e. if a < b then, a+xb+x>ab where x is any natural number.


Example : The ratio between two numbers is 12 : 13. If each number is reduced by 20, the ratio becomes 2 : 3. Find the numbers.

Solution:
Let the numbers be 12x and 13x

∴ 12x-2013x-20=23

⇒ x = 2    

∴ Numbers are 24, 26.


Example : If bc : ac : ab = 1 : 2 : 3, find a/bc ∶b/ca

Solutionbcac=12⇒ a ∶ b = 2 ∶ 1.

∴ abc:bca=abc×cab=a2b2=41


When the ratio is expressed in terms of fractions, we multiply all the terms with LCM of denominators to simplify the ratio.


Example : A person distributes his pens among four friends A, B, C and D in the ratio 13 : 141516. What is the minimum number of pens that the person should have?

Solution:
LCM of 3, 4, 5 and 6 is 60. Hence, we multiply all terms with 60.

So, the pens are distributed among A, B, C and D in the ratio 1/3 × 60 ∶ 1/4 × 60 : 1/5 × 60 ∶ 1/6 × 60

i.e. 20 : 15 : 12 : 10

∴ Total number of pens = 20x + 15x + 12x + 10x = 57x

For minimum number of pens, x = 1

∴ The person should have at least 57 pens.


Example : A bag contains 25 paise, 10 paise and 5 paise coins in the ratio 1 : 2 : 3. If their total value is Rs. 30, the number of 5 paise coins is :

Solution:
Let the number of coins be x, 2x and 3x

Value of 'x' 25 paise coins = 25x, that of '2x' 10 paise coins = 2x × 10 and that of '3x' 5 paise coins = 3x × 5.

Since, the total value is Rs. 30.

⇒ x × 25 + 2x × 10 + 3x × 5 = 30 × 100 (converting all the amounts in paise)

⇒ 60x = 3000    

i.e. x = 50

∴ Number of 5 paise coins are 3x = 150.


Example : Two numbers are in the ratio 3 : 7 and if 6 be added to each of them, they are in the ratio 5 : 9, then find the numbers.

Solution:
Let the numbers be 3x and 7x

∴ 3x+67x+6=59 or 27x + 54 = 35x + 30

or 8x = 24 i.e., x = 3

Numbers are 3 × 3; 7 × 3 i.e., 9 and 21.


Example : A profit of Rs. 84 is divided between A and B in the ratio of 1314. What will be the difference of their profits?

Solution:
1314 is the same as 13 × 12 ∶ 14 × 12 i.e., 4 : 3

Share of A = 4/7 × Rs. 84 = Rs. 48

Share of B = 3/7 × Rs. 84 = Rs. 36

Difference = Rs. 48 – Rs. 36 = Rs. 12


Example : The ratio of ages of Meera and Meena is 4 : 3. The sum of their ages is 28 years. The ratio of their ages after 8 years will be :

Solution:
Age of Meena = 4/7 × 28 = 16 years

Age of Meera = 3/7 × 28 = 12 years

After 8 years their respective ages will be 24 years and 20 years which shall be in the ratio 24 : 20 or 6 : 5


Example : A man divided Rs. 2,60,000 amongst his three daughters such that four times the amount received by the first, thrice the amount received by the second and twice the amount received the third are all equal. Find the amount received by the third daughter.

Solution:
Let the amounts received by first, second and third daughter by x, y and z respectively.

Hence, 4x = 3y = 2z.

We divided all the expression by LCM of coefficients i.e., LCM(4, 3, 2) = 12

⇒ x/3 = y/4 = z/6

Now assuming, x/3 = y/4 = z/6 = k
⇒ x = 3k, y = 4k and z = 6k

∴ x : y : z = 3k : 4k : 6k = 3 : 4 : 6

∴ Third daughter’s share = 6/13 × 2,60,000 = 12,000.

When two or more ratios are equal then ratio of numerators is same as the ratio of denominators.

If ap = bq = cr

then, a : b : c = p : q : r

 

Combining 2 or more ratios :

There may be situations where there are more than two quantities and they are not in the same ratio. The ratios can be scaled to find a common ratio.


Example : ab = 23 and bc = 34. Find a : b : c.

Solution:
Here, calculating combined ratio is very simple.

For every 2 parts of a, there are 3 parts of b and for every 3 parts of b, there are 4 parts of a.

Hence, for every 2 parts of a, there are 3 parts of b and 4 parts of c.

∴ a : b : c = 2 : 3 : 4


In the previous Example, the value of the common term ‘b’ was same hence, it was easy to calculate the combined ratio.

What if the value of the common term is not same :


Example : ab = 23 and bc = 45. Find a : b : c.

Solution:
Here, since the common term ‘b’ has different values, we will first have to make its value same in both the ratios,

i.e. is equal to LCM of the two values.

ab = 23 = 812 (Multiplying 4 in both numerator and denominator)

bc = 45 = 1215 (Multiplying 3 in both numerator and denominator)

Now, for every 8 parts of a, there are 12 parts of b and 15 parts of c.

∴ a : b : c = 8 : 12 : 15

We can extend this logic to combine more than 2 ratios also but that would require a lot of effort and time. 

There exists an easier and quicker method of solving the same.

If ab=n1d1, bc=n2d2, cd=n3d3 and de=n4d4 

Then, a : b : c : d : e = (n1 × n2 × n3 × n4) : (d1 × n2 × n3 × n4) : (d1 × d2 × n3 × n4) : (d1 × d2 × d3 × n4) : (d1 × d2 × d3 × d4)


Example : ab = 23, bc = 45, cd = 12 and de = 21. Find a : b : c : d : e.

Solution: Here, a : b : c : d : e = (n1 × n2 × n3 × n4) : (d1 × n2 × n3 × n4) : (d1 × d2 × n3 × n4) : (d1 × d2 × d3 × n4) : (d1 × d2 × d3 × d4)

⇒ a : b : c : d : e = 2 × 4 × 1 × 2 : 3 × 4 × 1 × 2 : 3 × 5 × 1 × 2 : 3 × 5 × 2 × 2 : 3 × 5 × 2 × 1.

⇒ a : b : c : d : e = 16 : 24 : 30 : 60 : 30.

⇒ a : b : c : d : e = 8 : 12 : 15 : 30 : 15


SOME USEFUL FORMULAE
For a given ratio ab
  • Duplicate ratio of ab = ab2

  • Triplicate ratio of ab = ab3

  • Sub-Duplicate ratio of ab = ab

  • Sub-Triplicate ratio of ab = ab3

  • Inverse/Reciprocal ratio of a : b = 1a : 1b

 

PROPORTION

Four quantities are said to be proportional, when the ratio of the first to the second is equal to the ratio of the third to the fourth.

Thus, a, b, c, d are proportional if a : b = c : d. This is often expressed as a : b :: c : d and is read ‘a’ is to ‘b’ as ‘c’ is to ‘d’.

The terms a and d are called the extremes and the terms b and c, the means.

The term d is called fourth proportional to a, b, c


Example : If 0.75 : x :: 5 : 8 then find x.

Solution:
Product of extremes = product of mean terms

0.75 × 8 = x × 5

⇒ x = 1.2


Example : The ratio of number of boys and girls in a school in 4 : 3. If there are 480 boys in the school, find the number of girls in the school.

Solution:
4 : 3 = 480 : x

⇒ (3 × 480)/4 = 360 girls

 

CONTINUED PROPORTION

Three or more quantities are said to be in continued proportion, when the first is to the second as the second is to the third, as the third is to the fourth; and so on. Thus, a, b, c, d are in continued proportion when

a : b = b : c = c : d

If three quantities a, b, c are in continued proportion (a : b :: b : c) then b is called the mean proportional between a and c.

i.e. ab=bc ⇒ b = √ac

and c is called third proportional to a and b.


Example : The mean proportion of 0.32 and 0.02 is what?

Solution:
If x be the required mean proportional then,

0.32 : x :: x : 0.02

⇒ x= 0.32 × 0.02

⇒ x = 0.08


Example : Find the third proportional to 16 and 24.

Solution:
16 : 24 :: 24 : x

⇒ x = (24 × 24)/16 = 36


Example : The sum of the squares of 3 numbers is 532 and the ratio of the first to the second as also of the second to the third is 3 : 2. What is the second number?

SolutionFirst numberSecond number=32×33=96 and Second numberThird number=32×22=64

[Make the second number same in both the ratios, i.e. 6]

∴ First : Second : Third = 9 : 6 : 4

∴ (9x)2 + (6x)2 + (4x)2 = 532 (given)

⇒ 133 x 2 = 532

⇒ x = 2

Second number is 6x = 12



Example : Rs. 3000 are divided amongst A, B and C so that if Rs. 20, Rs. 40 and Rs. 60 be taken from their shares respectively, they will have money in the ratio 3 : 4 : 5. Find the share of C.

Solution:
Total decrease = Rs. 20 + Rs. 40 + Rs. 60 = Rs. 120

Remaining sum = Rs. 3000 – Rs. 120 = Rs. 2880

C’s share = 5/12 × Rs. 2880 = Rs. 5 × 240 = Rs. 1200

∴ Share of C out of Rs. 3000 = Rs. 1200 + Rs. 60 = Rs. 1260


Example : Rs. 4400 are divided among A, B and C so that A receives 3/8 as much as B and C together. What is the share of A?

Solution:
when (B + C) get Rs. 1, A gets Rs. 3/8

∴ A’s share : (B + C)’s share = 3/8 : 1 = 3∶8

∴ A’s share = Rs. 311 × 4400 = Rs. 1200


Example : The ratio of the first and second class fares between the two stations is 4 : 1 and that the number of passengers travelling by first and second class is 1 : 40. If Rs. 1100 is collected as fare, the amount collected from first class passengers is :

Solution:
Ratio of amounts collected from 1st and 2nd class = (4 × 1) : (1 × 40) = 1 : 10

∴ Amount collected from 1st class passengers = 111 × Rs. 1100 = Rs. 100


Example : One year ago the ratio between Laxman’s and Gopal’s salary was 3 : 4. The ratio of their individual salaries between last year’s and this year’s salaries are 4 : 5 and 2 : 3 respectively. At present the total of their salary is Rs. 4160. The salary of Laxman now is :

Solution:
Let the salaries of Laxman and Gopal one year before be a, b respectively and now c, d respectively.

⇒ a : b = 3 : 4

a : c = 4 : 5

b : d = 2 : 3

It is given that c + d = 4160

ab = 34; ac = 45 and bd = 2/3

Let a be 3x and b be 4x.

Hence, c = 15x/4 and d = 6x

⇒ c ∶ d = 15x46x=58

∵ c + d = 4160

∴ c = 513 × 4160 = Rs. 1600.

 

 

PARTNERSHIP

If two or more persons invest their money (capital) in a joint business, their association is called partnership. 

A partner who simply invests money but does not attend to the business is called a silent / sleeping partner. One who invests money as well as attends to the business is a working partner.

Such type of questions require us to distribute profit among partners. 

Profit is directly proportional to investment when everyone invests for same amount of time.

Profit is also directly proportional to time invested when everyone invests for the same amount.

Hence, Profit ∝ Investment × Time

Generally, the gain or loss is divided among the partners in a partnership on the basis of the following rule:

PAPB = IA×TAIB×TB

where,
IA = Investment of A
IB = Investment of B
TA = Time of Investment of A
TB = Time of Investment of B


Example : Ram and Shyam enter into a partnership. Ram invests Rs. 24,000 and Shyam invests Rs. 20,000. Find the share of each in a Profit of Rs. 66,000 after one year.

Solution:
Ratio of investments of Ram and Shyam = 24,000 : 20,000 = 6 : 5

Ram’s share in a profit of Rs. 66,000 = Rs. 611 × 66000 = Rs. 36,000

Shyam’s share = Rs. 511 × 66000 = Rs. 30,000


Example : Ram and Shyam enter into a partnership with same investment. Ram invests for 8 months and leaves the business. Find the ratio of share of each after one year.

Solution:
Ratio of profits of Ram and Shyam = I × 8 : I × 12 = 2 : 3


Example : Ram, Mohinder and Jatinder enter into a partnership. Ram invests Rs. 24,000, Mohinder Rs. 20,000 and Jatinder Rs. 30,000. Find the share of each in a profit of Rs. 74,000 after one year.

Solution:
Ratio of investments of Ram, Mohinder & Jatinder = 24,000 : 20,000 : 30,000 = 12 : 10 : 15

Ram’s share in a profit of Rs. 74,000 = Rs. 12/37 × 74000 = Rs. 24,000

Mohinder’s share = Rs. 10/37 × 74000 = Rs. 20,000

Jatinder’s share = 15/37 × 74000 = Rs. 30,000.


Example : Ram, Mohinder and Jatinder enter into a partnership. Ram invests Rs. 24,000 for 8 months, Mohinder Rs. 20,000 for 12 months and Jatinder Rs. 30,000 for 6 months. Find the share of each in a profit of Rs. 51,000 after one year.

Solution:
Ratio of profits of Ram, Mohinder & Jatinder = 24,000 × 8 : 20,000 × 12 : 30,000 × 6 = 16 : 20 : 15

Ram’s share in a profit of Rs. 51,000 = Rs. 16/51 × 51000 = Rs. 16,000

Mohinder’s share = Rs. 20/51 × 51000 = Rs. 20,000

Jatinder’s share = 15/51 × 51000 = Rs. 15,000.


Example : Rajkumar and Sandeep entered into a partnership investing Rs. 48,000 and Rs. 54,000 respectively. After 3 months Jugal Kishore also joined the business with a capital of Rs. 40,000. Find the share of each in a profit of Rs. 55,000 after a year.

Solution:
Ratio of profits of Raj Kumar, Sandeep and Jugal Kishore :
48000 × 12 : 54000 × 12 : 40000 × 9 = 8 : 9 : 5

Raj Kumar’s share in the profit = Rs. 822 × 55,000 = Rs. 20,000

Sandeep’s share in the profit = Rs. 922 × 55,000 = Rs. 22,500

Jugal Kishore’s share = Rs. 522 × 55000 = Rs. 12,500


Example : P, Q and R contract a work for Rs. 1100. P and Q together are to do 711 of the work. Find R’s share of the amount contracted for.

Solution:
R’s share of work = 1 - 711 = 411 of the total work.

Since R does 4/11th of the total work, he would receive 4/11th of the total amount as well.

∴ R’s share in total money = 411 × 1100 = Rs. 400.


Example : In a partnership, A invests 1/6 of the capital for 1/6 of the time, B invests 1/3 of the capital for 1/3 of the time and C, the rest of the capital for whole time. Find A’s share of the total profit of Rs. 2,300.

Solution:
Capital of C = 1 - 1/6 - 1/3 = 1/2

Let the total time be 12 months

∴ A’s profit : B’s profit : C’s profit

16×16×12  : 13×13×12 : 12×12 = 13 : 43 : 6 = 1 : 4 : 18

∴ Share of A = 11+4+18 × 2300 = Rs. 100.

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