Answer:
5 : 1
Step-by-step explanation:
From your second-grade memorization of multiplication tables, you recognize that 15 = 3×5, so you know 3 is a factor of both numbers in the ratio. To reduce the ratio to simplest form, you divide out all common factors:
15 : 3 = (15/3) : (3/3) = 5 : 1
