Answer is 9:7
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Step-by-step explanation
There are 32 marbles and 14 are red. If there are only two colors, then we have 32-14 = 18 blue marbles.
The ratio of blue to red is 18:14. We write the two values separated by a colon. The order matters (blue comes first, then red).
The last step is to reduce the ratio 18:14 to 9:7. Note how I divided both parts by the GCF 2.