Question

Find the sum of all 3 digit numbers which are multiples of 5

Answer 1

The 3 digits are 100 to 999
The first 3 digit number which is multiple of 5 is 100 and the last is 995

100, 105, 110, 115, ...... 990, 995
We need to find sum of these numbers
a = 100
d = 5
aₙ = a + (n-1)d
995 = 100 + (n-1)5
895 = (n-1)5
179 = n-1
n = 180

Sₙ = n/2[2a + (n-1)d]
= 90[200 + 179(5)]
= 90[200 + 895]
= 90(1095)
= 98550

Answer 2

hey mate here is your ans.