An easy question on numbers

A four-digit number has the following properties:

(a) It is a perfect square;

(b) Its first two digits are equal

(c) Its last two digits are equal.

Find all such four-digit numbers. (RMO '91)

2 Answers

106
Asish Mahapatra ·

it is evidently divisible by 11
let the no be aabb
then dividing by 11 we get a0b which is again divisible by 11
so a+b equals 11

now u get only few options out of which 7744 satisfies perfect square

106
Asish Mahapatra ·

(100a + b)/11
(100a + 11 - a)/11
9a + 1
this must be a perfect square u get only a is 7

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