Explanation:

All positive integral multiples of 2 less than 100 are – 

     2,4,6,……,98 

This is in AP with a =2 ,d=2 and l = 98 

Now , l = a +(n-1)d 

98 = 2 + (n-1)×2 

2n = 98 

Or  n = 49 

Thus , sum S = 49/2 [2+98] 

= 49×100/2 

= 2450