Question

Each marble bag sold by Rachel's Marble Company contains 3 purple marbles for every 2 green marbles. If a bag has 21 purple marbles, how many green marbles does it contain?

Answer 1

The ratio is 3:2, purple :green
The bag has 21 purple so to get from 3 to 21 it is multiplied by 7; so we must also multiply the 2 by 7 to keep the ratio balanced.
21:14