Question

Using AP, find the sum of all 3-digit natural number which are multiple of 7.

Answer 1

Answer:

Step-by-step explanation:

First three digit term divisible by 7 is 105

Last three digit term divisible by 7 is 994

We know that tn=a+(n−1)d

⇒994=105+(n−1)7

⇒n=128

We know that Sn=n/2(l+a)

∴ The sum of the required series Sn=1282(994+105)

=64×1099=70336

Answer 2

hey buddy...
IN AP...the formula for sum of number no is...n/2(a+l)
here the a(first number) is...7×15 = 105...
and the l(last number) is...7×142 = 994...
so n is the number B/W 142 - 15= 127
so by formula..
127/2 ×(105+994)= 127/2×1099
therefore the ans..plss calculate..!!
hope this will help u bro!!!