Question

the sum of integers from 1 to 100 that are divisible by 2 or 5 is:

Answer 1

sum of integers from 1 to 100 that are divisible by 2
=n(n+1) =50*51 =2550
sum of integers from 1 to 100 that are divisible by 5 but not divisible by 2. are 5,15,.25,----------95
= 10/2 (5+95) = 500
The sum of integers from 1 to 100 that are divisible by 2 or 5 is=2550+500=3050 is the answer

Answer 2

the series formed divi by 2 : 2, 4 , 6 .... 100
by using formula An = A + (n-1)d
            here An = 100 , A = 2
                     n = 50 
then by using formula Sn = n/2 (2a + (n-1)d)
   by putting values Sn = 2500 
the series formed divi by 5 : 5, 10, 15 .... 100
                   here n = 20 
and  Sn = 1050