Of the 7 numbers, average of first 4 numbers is 25 while that of the last 4 numbers is 31. Average of all 7 numbers is 28. Find the 4th number.
Explanation:
Sum of all the 7 numbers = 28 × 7 = 196
Sum of first 4 numbers = 25 × 4 = 100 Sum of last 4 numbers = 31 × 4 = 124
⇒ Sum of first 4 numbers + sum of last 4 numbers – 4th number = Sum of all 7 numbers.
⇒ 100 + 124 – 4th number = 196
⇒ 4th number = 224 – 203 = 28.
Hence, option (a).
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