A jar contains only red and blue marbles in a ratio of 3:9. If there are 63 blue marbles, how many red marbles are there?

Correct answer

A. 21

Explanation

The ratio 3:9 means for every 9 blue marbles there are 3 red. 63 blue ÷ 9 = 7 groups, so red marbles = 3 × 7 = 21.

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