Consider perfect squares whose unit digit is 4, such as 144 and 324.
Among the squares from $1^{2}$ to $2 0^{2}$ , how many end in the digit 4?

Question

Consider perfect squares whose unit digit is 4, such as 144 and 324. Among the squares from 1^2 to 20^2, how many end in the digit 4?

Accepted Answer

4. A square ends in 4 when the number ends in 2 or 8. From 1 to 20: 2, 8, 12, 18 — that is 4 numbers (4, 64, 144, 324).

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