Question

If sum of three continuous multiples of 13 is 390, then what are they?​

Answer 1

Answer:

What is the sum of all natural numbers between 100 and 400 which are divisible by 13?

Firstly try to find the number between 100 and 400 which are actually divisible by 13 so

104,117,130………. 390

If you see the above arrangement the difference between numbers are common so we can apply arithmetic progression.

By arithmetic progression, last term can be denoted by

l= a+(n-1)d

Where l=390

a=104

d=13

n=?

390=104+(n-1)13

13n=286+13

n= 299/13

n= 23

So total number of terms =23

By using arithmetic progression sum of all A.P terms = (n/2)(a+l)

Sum = (23/2)(104+390)

=(23/2)*(494)

= 5,681

So answers is 5,681.