Let number of a pairs of brown socks = y Price of brown socks = x Price of black socks = 3x According to question ⇒ 5 × 3x + yx = 100 ... (i) Now, clerk has interchanged socks pairs then price is increased by 100% 3xy+5x=(15x+yx)+
(15x+yx)×100
100
= 3xy + 5x = 30x + 2xy ... (ii) ⇒ 30x + 2yx = 3xy + 5x ⇒ 25x = xy y = 25 ∴ So, number of brown socks = 25