Q. Find the squares of the following numbers containing 5 in unit’s place.

(i) 15

Answers (1)

Assume a number with unit digit 5 = a5

(a5)^{2} = (10a + 5)^{2} = 10a(10a + 5) + 5(10a + 5) = 100a 2 + 50a + 50a + 25

                            = 100a(a + 1) + 25

                            = a(a + 1) hundred + 25

We will use this result here,

We have a5 = 15 , So a = 1

(15)^{2} = 1(1+1)100 + 25 = 200 + 25 = 225

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