A jar contains only red and blue marbles in a ratio of 4:7. If there are 21 blue marbles, how many red marbles are there?

Correct answer

B. 12

Explanation

The ratio 4:7 means for every 7 blue marbles there are 4 red. 21 blue ÷ 7 = 3 groups, so red marbles = 4 × 3 = 12.

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