Question

2. Find the sum of all numbers from 1 to 140 which are divisible by 4.
​

Answer 1

Answer:

Clearly, the numbers from 1 to 140 which are divisible by 4 are 4,8,12,...140.  

This  is an AP with first term a=4, common difference d=4 and last term l=140.

Let there be n terms in this AP.  

Then,

a  

n

​  

=140⇒a+(n−1)d

140=4+(n−1)×4

∴n=35

∴  required sum =S  

n

​  

=  

2

n

​  

[a+l]=  

2

35

​  

[4+140]

=2520

hope it helped....