The price of raw materials has gone up by 15%, labour cost has also increased from 25% of the cost of raw material to 30% of the cost of raw material. By how much percentage should there be reduction in the usage of raw materials so as to keep the cost same?

Explanation:-

Let the initial cost of raw material be 100. So, initial labour cost was 25 and net cost was 125.
Now,
15% increment in raw materials cost and labour cost has gone up to 30% from 25 %.
Raw material cost = 115. And
Labour cost = (115 *30) = 34.5
So, New net cost,
= 115 + 34.5 = 149.5
%reduction = 24.5/149.5 = 17%(approx.)