Question

The sum of first twenty terms of A.P which are divisble by both 2 and 5 is​

Answer 1

Answer:

2100

Step-by-step explanation:

The no. of terms divisible by both 2and5 :-

10,20,30,..............

Sum of the terms:-

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

Since there are 20 terms so n = 20, a = 10,

d = 10(20-10)

Substituting the values

Sn = 20/2(2*10 + (20-1)*10)

Sn = 10(20 + 190)

Sn = 10*210

Sn = 2100 ans