Question

find the sum of all natural numbers less than 200 which are divisible by 5​

Answer 1

here natural no. which are divisible by 5 and less than 200

5,10,15,......195 this is an AP.

here ,

a=5 , d=5 , tn= 195

we know ,

tn=a+(n-1)d

195=5+(n-1)5

195=5+5n-5

195=5n

n=195/5

n=39

now,

Sn=n/2{2a+(n-1)d}

Sn=39/2{10+38×5}

Sn=39/2×200

Sn=39+×100

Sn=3900

therefore the sum of natural no.which are divisible by 5 and less than 200 is 3900