Q. Find the squares of the following numbers containing 5 in unit’s place.
(iv) 205
Consider a number with unit digit 5, i.e., a5
= = 10a(10a + 5) + 5(10a + 5) = 100a 2 + 50a + 50a + 25
= 100a(a + 1) + 25
= a(a + 1) hundred + 25.
Here a = 20
Hence = 20(20+1)hundred + 25
= 20(21)hundred + 25 = 42000 + 25
= 42025