EduGoog

Given set : (9, 15, 21)

Option:
A. (10, 14, 16)
B. (7, 21, 28)
C. (5, 10, 25)
D. (4, 8, 12)
Answer: D . (4, 8, 12)

Justification: In each set, 1st number + 3rd number / 2 = 2nd number.

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