A person ordered 5 pairs of black socks and some pairs of brown socks

A person ordered 5 pairs of black socks and some pairs of brown socks. The price of a black pair was thrice that of a brown pair. While preparing the bill, the bill clerk interchanged the number of black and brown pairs by mistake which increased the bill by 100%. What was the number of pairs of brown socks in the original order?

  1. 15
  2. 25
  3. 10
  4. 20

Answer

Price of Brown socks = p

Price of Black socks = 3p

Let number of brown socks ordered be n.

Wrong Bill is 100% more means it is twice than the correct bill.

n*3p + 5*p = 2(n*p + 5*3p)

3n + 5 = 2n + 30

n = 25

The correct option is B.