Question

Find sum of all natural number between 1 and 201 which is divisible by 5​

Answer 1

First number between 1 and 201 i.e. divisible by 5= a =5

Last number divisible by 5 = an= 200

Common difference = d = 5

an = a + (n-1)d

200 = 5 + (n-1)5

195 = 5(n-1)

39 = n-1

n = 40

Therefore,there are 40 numbers between 1 and 201 divisible by 5.

Now S40= 40/2[2×5 + 39×5]

S40= 20[10 + 195)

S40= 20 × 205

S40= 4100

Therefore, sum of all no.s divisible by 5 between 1 and 201 is 4100.