A clock was sold for Tk. 144. If the percentage of profit was numerically equal to the cost price, the cost of the clock was -

Question: A clock was sold for Tk. 144. If the percentage of profit was numerically equal to the cost price, the cost of the clock was -

Solution:
Let, the percentage of profit be x%
cost of the clock was x taka.

x + x × x/100 = 144
⇒ x + (x²/100) = 144
⇒ (x² + 100x) = 14400
⇒ x² + 100x - 14400 = 0
⇒ x² + 180x - 80x - 14400 = 0
⇒ x(x + 180) - 80 (x + 180) = 0
⇒ (x + 180) (x - 80) = 0
⇒ x = 80