Question

find the sum of all integers between 1 to 500 which are multiples of 2 or 5​

Answer 1

for multiples of 2
Sn=?
d=2
a=2
an=500
n=?
we know, an=a+(n-1)d
So,
500=2+(n-1)2
498/2=n-1
249=n-1
n=250
We know, Sn=n/2[2a+(n-1)d]
So,
Sn=250/2[2(2) + (250-1)2]
Sn=125[4+498]
Sn=125(502)
Sn=62750
Ans. 62750

For divisible by 5 do same process but the take common difference (d) and first term(a) as 5.