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प्रश्न
Find the sum of first 12 natural numbers each of which is a multiple of 7.
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उत्तर
First 12 natural numbers which are multiple of 7 are as follows:
7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84
Clearly, this forms an A.P. with first term a = 7,
Common difference d = 7 and last term l = 84
Sum of first n terms = `S = n/2 [a + l]`
`=>` Sum of first 12 natural numbers which are multiple of 7
= `12/2 [7 + 84]`
= 6 × 91
= 546
संबंधित प्रश्न
In an AP, given a = 2, d = 8, and Sn = 90, find n and an.
The first term of an A.P. is 5, the last term is 45 and the sum is 400. Find the number of terms and the common difference.
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Find the sum of the following arithmetic progressions: 50, 46, 42, ... to 10 terms
Find the 6th term form the end of the AP 17, 14, 11, ……, (-40).
Find the sum of first n terms of an AP whose nth term is (5 - 6n). Hence, find the sum of its first 20 terms.
Q.1
Find the common difference of an A.P. whose first term is 5 and the sum of first four terms is half the sum of next four terms.
Find the sum of those integers from 1 to 500 which are multiples of 2 or 5.
[Hint (iii) : These numbers will be : multiples of 2 + multiples of 5 – multiples of 2 as well as of 5]
Find the sum of last ten terms of the AP: 8, 10, 12,.., 126.
