Answer:
12
Explanation:
The least common multiple (LCM) of 3 and 4 is 12. Adam would have to divide each rectangle into a minimum of 12 parts.
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His shading would be 4 parts (4/12 = 1/3) of one of them and 3 parts (3/12 = 1/4) of the other.
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3 and 4 have no common factors, so their LCM is their product. 3×4 = 12.