Question

Numbers that cannot come at unit's place in a perfect square

Answer 1

Numbers that can't come at unit place after perfect square are:-

2,3,7 and 8.

Because if we check squares of 10 natural numbers then we came to know that these numbers never comes at unit place.

${1}^{2} = 1 \\ {2}^{2} = 4 \\ {3}^{2} = 9 \\ {4}^{2} = 16(unit \: digit \: 6) \\ {5}^{2} = 25(unit \: digit \: 5) \\ {6}^{2} = 36(unit \: digit \: 6) \\ {7}^{2} = 49(unit \: digit \: 9) \\ {8}^{2} = 64(unit \: digit \: 4) \\ {9}^{2} = 81 \: (unit \: digit \: 1)$
so the numbers will be ●●●2,3,7 and 8●●●