Question

a person sold his watch for Rs24 and got a percentage of profit equal to the cost price, then the cost price is

Answer 1

Let the cost price be x.
So,
x*(100+x)/100=24.
=>100x+x^2=2400
=>x2+100x-2400=0
=>x2+120x-20x-2400=0
=>x(x+120)-20(x+120)=0
=>(x-20)(x+120)=0
So, either
x-20 = 0. OR. x+120=0
=>x=20. OR. =>x=-120
But cost price cannot be negative. So the cost price is Rs.20.(Positive value of x)

Answer 2

Hello friend

Let us assume the cost price be x

Profit percentage is x%

Profit %= profit/cost price * 100

x=(24-x)/x * 100

x²=2400-100x

x²+100x-2400=0

x²+120x-20x-2400=0

x(x+120)-20(x+120)=0

(x-20)(x+120)=0

x can be 20 or -120

As money can't be negative, x is 20

Cost price is rs.20