Question

Q.21 A sold a watch at 10% profit. If he
bought if at 10% less and sold it for Rs.15
more, he would have gained 25%. Find the
cost price of watch.​

Answer 1

Price of watch is 45 he sold it 60 rupees he gain 25%

Answer 2

The cost price of the watch is Rs 120.

Let cost price of the watch be Rs x.

He sells it a profit of 10%.

So, SP = (100+profit)% of CP

= (100+10)% of Rs x

= Rs 1.1x

When CP was 10% less, that is 90% of x = Rs 0.9x

SP = Rs 15 more.

So, SP = Rs 15 + Previous CP

= Rs (15 + x)

Profit = SP-CP = Rs (15+x - 0.9x) = Rs (0.1x + 15)

Profit%  = [Profit/CP]×100%

= [(0.1x + 15)/0.9x]×100%

Given this is equal to 25%

So, [(0.1x + 15)/0.9x]×100 = 25

⇒0.9x = 4[0.1x + 15]

⇒0.9x =  0.4x + 60

⇒0.5x = 60

⇒x = 60×0.5 = Rs 120

This is the cost price.