Question

A stationer gains 20% by selling pens at 12 for Rs.72. How many pens should he sell for Rs.100. to gain 25%?

Answer 1

S.P. of 12pens = Rs.72
∴ S.P. of 1 pen
= Rs. `(72)/(12)`
= Rs.6
Gain % = 20%
`"S.P."/"C.P." = 1 + "Profit"/(100)`

⇒ `(6)/"C.P." = 1 + (20)/(100)`

⇒ `(6)/"C.P." = (100 + 20)/(100)`

⇒ C.P. = `(100)/(120) xx 6`
= Rs.5
Given, S.P. = Rs.100
Gain = 25%
`"S.P."/"C.P." = 1 + "Profit"/(100)`

⇒ `(100)/"C.P." = 1 + (25)/(100)`

⇒ `(100)/"C.P." = (100 + 25)/(100)`

⇒ C.P. = `(100)/(125) xx 100`
= Rs.80
∴ Number of pens sold
= `("Rs".80)/("Rs".5)`
= 16.