Toshiba bought 100 hens for Rs 8000 and sold 20 of these at a gain of 5%. At what gain percent she must sell the remaining hens so as to gain 20% on the whole?

Explanation

CP of 1 hen=8000/100=80Rs

Profit percentage=profit/CP=`(SP-CP)/(CP)`

`5/100=(SP-80)/80`

SP=84 for 20 hens

`20%=((SP)/100-(CP)/100)/((CP)/100)`

`SP=80+400=480Rs`

Gains percentage on remaining=`(396-320)/320*100`

=23.75%.