A farmer bought 100 hens for ₹4000, sells 20 of them at a gain of 5%. At what gain % must he sell so as to gain 20% on the whole?
From question,
Price of 100 hen =₹4000
Price of 1 hen =4000100=₹40
He sells 20 hens at a gain of 5%
So, selling price of those 20 hens =20×[100+Profit %100×C.P]
=20×[100+5100×40]
=20×[105100×40]
=20×[1055×2]
=20×[21×2]
=20×42
=₹840
On the whole he wants 20% profit which means the profit he wants =20100×4000
=20×40
=₹800
Price of 80 hens =80×40=₹3200
From ₹800 he already got Profit Of ₹40 Which Means he has to get More ₹760
Gain Percentage (%)=ProfitC.P×100
=7603200×100
=198
=23.75%
Hence, the required gain percentage =23.75%