An Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE Board.

This is the Question Number 11 Exercise 11 C of RS Aggarwal Solution.

Here you have to find the all multiples of given digit which is lying between the given numbers.

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# Find the sum of all multiples of 9 lying between 300 and 700.

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The multiples of 9 between 300 and 700 :-

306 , 315 , 324 ,â€¦.., 693

First term = 306

Common difference = 9

nth term = 693a_n=a+(n-1)d

693 = 306 + (n – 1)9

693-306/9=n-1

n-1=387/9

(n – 1) = 43

n = 43 + 1

n = 44

Using formula :-

S_n=n/2(a+l)

S_44=44/2(306+693)

= 22 Ã— 999

= 21978