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Question

The square of number 85 is:


A

7115

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B

7205

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C

7225

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D

7375

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Solution

The correct option is C

7225


Consider a number with unit digit 5, i.e., a5

(a5)2 = (10a + 5)2
= 10a(10a + 5) + 5(10a + 5)
= 100a2 + 50a + 50a + 25
= 100a(a + 1) + 25
= a(a + 1) hundred + 25

Hence, (85)2 = 8(8+1) x 100 + 25 = 7225


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