Question

The sum of all the multiples of 7 lying between 500 and 800 is:​

Answer 1

Answer:

The list of numbers between 500 and 800 that are multiples of 7 is :

504, 511, 518,.........................798.

Clearly the above list is in AP with first term, a = 504  and common difference, d = 7.

Let the nth term of AP is 798.

an = a + (n - 1)d

⇒ 798 = 504 + (n - 1)(7)

⇒ n = 43

sum of first 43 terms of the above AP is given by,

Answer 2

Step-by-step explanation:

now the AP is series of multiples with

a=504 , d=7 and L(last term )=798

thus no of multiples of 7 between 500 and 800

by using an =a +(n-1)d

798=504+(n-1)d

294=(n-1)7

so by solving ,n=43        

thus Sn=n/2(a+l)

so Sn=43/2(504+798)

         =27993

so the answer is 27993