Question

A vendor buys a certain number of pens. If the selling price of 5 pens is equal to the cost price of 7 pens, find his profit or loss percentage.

Answer 1

Consider Rs. x as the C.P. of 7 pens

C.P. of 1 pen =Rs.x/7

Based on the question

S.P. of 5 pens =Rs.x

S.P. of 1 pen =Rs.x/5

Profit=S.P.–C.P.

Substituting the values

=x/7–x/5

Taking LCM

=(7x–5x)/35

=Rs.2x/35

We know that

Profit%=Profit/C.P.×100%

Substituting the values

=

x/7

2x/35

×100 %

It can be written as

=2x/35×7/x×100 %

By further calculation

=2/5×100 %

So we get

=2×20 %

=40 %