Find the sum of all the integers between 120 and 400 (both inclusive) which are divisible by 7.
Solution: Option (e)
In between 120 and 400
The first number divisible by 7 = 126, Last number divisible by 7 = 399
The other numbers divisible by 7 are 126, 133, 140, 147... 399; All the numbers are in an AP with common difference of 7. Number of terms in the AP =(399−126)7+1+1=40
Sum of all the terms =(402)(126+399)=10500.