1.

Which of the following four digit numbers is a perfect square such that the first two digits and the last two digits considered separately also represent perfect squares ? (A) 1681 (B) 5462 (C) 8214 (D) 7210

Answer»

Correct option is (A) 1681

(A) 1681 = 1600+80+1 \(=40^2+2\times40\times1+1^2=(40+1)^2=41^2\)

\(\therefore\) 1681 is a perfect square.

Also, its first two digits \(=16=4^2\) is a perfect square.

And its last two digits \(=81=9^2\) is a perfect square.

Thus, 1681 is a type of required number.

(B) 5462 is not a perfect square because any number whose last digit (unit digit) is 2 never forms a perfect square.

Thus, 5462 is not a type of required number.

Similarly 8214 and 7210 are not a perfect square.

Thus, both are not a type of required number.

Correct option is (A) 1681



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