Question

A shopkeeper bought locks at the rate of 8 locks for Rs.520 and sold them at the rate of 12 locks for Rs.936. Calculate his gain or loss percent and the number of locks he should sell to earn a net profit of Rs.520.

Answer 1

Cost of 8 locks = Rs.520
∴ C.P. of 1 lock
= Rs.`(520)/(8)`
= Rs.65
Selling price of 12 locks = Rs.936
∴ S.P. of 1 lock 
= Rs.`(936)/(12)`
= Rs.78
∵ S.P. > C.P.
Profit 
= S.P. - C.P.
= Rs.(78 - 65)
= Rs.13
Profit%
= `"Profit"/"C.P." xx 100`

= `(13)/(65) xx 100`
= 20%
Net profit = Rs.520
∴ Number of locks sold
= `"Total profit"/"profit per lock"`

= `(520)/(13)`
= 40.