Sophia buys jellybeans at 5 for 3 cents, and sells them at 6 for 5 cents. How many must she sell in order to make a profit of $3.50?

1 jellybean costs 3/5¢ and sells for 5/6¢.

The profit per jellybean is 5/6¢ – 3/5¢ = (25 – 18)/30¢ = 7/30¢.

Sophia sells *x* jellybeans for a profit of $3.50 or 350¢.

(7/30)*x* = 350 → *x* = (350 · 30)/7 = 1500 jellybeans.