
Hi Sinha
In this question , let's say Total goods=100
This means 50 he sold at 30% profit (from cost price (the price for which he bought)).
next 25 sold at 15% discount from SELLING PRICE HE FIXED. Or in other words at 10.5% profit from Cost price.{First Cost price increased by 30% then reduced by 15% , so the net %change is 10.5% profit or increase from cost price or actual profit.
Next 25 sold at 30% discount from SELLING PRICE HE FIXED. OR at 9% loss from Cost price.(because first price increased by 30% then decreased by 30% so equivalent %change is 9% LOSS.)
U can solve this question by
1. By algebra
2. By plugging in values
3. By wieghted average concept etc..
so BY wieghted average it can be done as follows:
50(30)+25(10.5)+25(9)/100 = 15+([10.5]/4)(9/4)= 15.375%
[ on 50 things he got 30% profit, on 25 things he got 10.5% profit and on next 25 things he got 9%loss{ that's why negative sign} and then divided by total no. of things]
Hope this is clear. 