Question

A man purchased 150 pens at the rate of Rs 12 per pen. He sold 50 pens at a gain of 10%. At what gain percent must he sell the remaining pens, so as to gain 15% on the whole transaction?

Answer 1

C.P of 150 pens = 12 per pen = 12*150 = 1800
50 pens were sold at a gain of 10%
C.P of 50 pens = 12*50 = 600
S.P = C.P*(100+G)/100 = 600*110/100 = 660
Total gain to be made = 15%
Total S.P = C.P*(100+P)/100 = 1800*115/100 =  2070
Remaining (100 pens) S.P = 2070 - 660 = 1410
C.P of 100 pens = 12*100 = 1200
Gain = 1410-1200 = 210
Gain % = Gain/C.P * 100 = 210/1200 * 100 = 17.5%
Hence, the remaining pens should be sold at a profit of 17.5% 
Hope it helps.