Question

Find the sum of the number divisible by 7from 200 to 500

Answer 1

There are 43 numbers between 200 and 500 which are divisible by 7, ranging from

7 × 29 = 203 to

7 × 71 = 497

[The shortcut for finding the total terms is to divide both terms and ignoring remainders. But for lower limit you have to round it up, and for upper limit round it down]

I am trying a short formula. I don't know if it works or not.

I am adding the upper limit to lower limit (497 + 203) and find average of the two.

Average = 350

Sum = 350 × 43 = 15050