Discussion

Explanation:

Let p be the original price/unit, consumption q = 18 quintals 

And expenditure e = p × 18 quintals 

10% reduction in price means that new price = 0.9p

We are now required to find consumption x, such that 0.9px = p × 18

⇒ x = 18/0.9 = 20 quintal.

Alternately,

Let the % change in consumption be C%.

Net change in expenditure = 0 = -10 + C + $\frac{-10\times C}{100}$

Solving this we get C = 11.11%

Hence, new consumption = 18$\left(1+\frac{11.11}{100}\right)$ = 18$\left(1+\frac{1}{9}\right)$ = 18 × $\frac{10}{9}$ = 20 quintals.

Alternately,
Price becomes (1 - 10/100) = 9/10 times.

For expenditure to remain constant, consumption should become 10/9 times.

∴ consumption at lower price = 18 × 10/9 = 20 quintals.

Hence, option (a).

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