Multiple choice

A girl sold her pen for Rs. $39$ and got a percentage of profit numerically equal to the cost price. The cost price of that pen is :

  1. $130$
  2. $90$
  3. $60$
  4. $30$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let CP = x. Profit % = x. Profit = (x/100) * x = x^2/100. SP = CP + Profit = x + x^2/100 = 39. x^2 + 100x - 3900 = 0. (x + 130)(x - 30) = 0. Since CP must be positive, x = 30.

AI explanation

Let the cost price of the pen be Rs. x, so the profit percentage is also x%. Using the profit formula, the selling price equals cost price plus profit, giving the equation 39 equals x plus x squared divided by 100. Multiplying by 100 yields x squared plus 100x minus 3900 equals 0, which factors to x equals 30.

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