a dealer sells a toy for rs24 and gains as much

Question

A dealer sells a toy for Rs.24 and gains as much percent as the cost price of the toy. Find the cost price of the toy.

Ans:    Let the C.P be x

∴Gain = x%

⇒ Gain =x.  x/100

S.P = C.P +Gain

SP = 24

x + x²/100 =24

On solving x=20 or -120 (rej)

∴C.P of toy = Rs.20