Answer: Consecutive numbers: 20, 21, 22
Explanation:
Three consecutive whole numbers: x, x+1, x+2
Avg. = [x + (x + 1) + (x + 2)] / 3 = 21
[3x + 3] / 3 = 21
3x + 3 = 63
3x = 60
x = 20
x + 1 = 21, x + 2 = 22
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