alleryHow many non-square natural numbers lie between 9² and 10² (exclusive of both)?
A9
B10
C18
D20
Answer & Solution
Correct answer: C. 18
Between n² and (n+1)² there are exactly 2n non-square numbers.
Here n = 9, so 2 × 9 = 18 non-squares lie strictly between 81 and 100.
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