There is a jar of green and red marbles. If there are 21 marbles total and the ratio of green to red is 3:4, how many red marbles are there?

There are 12 red marbles

Step-by-step explanation:

green : red : total

3           4       3+4=7

We want a total of 21

21 /7 =3

Multiply by 3

green : red : total

3*3       4*3   7*3

 9         12     21

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14

step-by-step explanation:

14 x 3 = 42