Advertisements
Advertisements
प्रश्न
Find the sum of first 12 natural numbers each of which is a multiple of 7.
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
APPEARS IN
संबंधित प्रश्न
How many terms of the A.P. 27, 24, 21, .... should be taken so that their sum is zero?
If the mth term of an A.P. is 1/n and the nth term is 1/m, show that the sum of mn terms is (mn + 1)
Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 respectively.
How many terms of the AP 63, 60, 57, 54, ….. must be taken so that their sum is 693? Explain the double answer.
Choose the correct alternative answer for the following question .
If for any A.P. d = 5 then t18 – t13 = ....
The first and the last terms of an A.P. are 8 and 350 respectively. If its common difference is 9, how many terms are there and what is their sum?
The given terms are 2k + 1, 3k + 3 and 5k − 1. find AP.
Q.11
Q.13
Obtain the sum of the first 56 terms of an A.P. whose 18th and 39th terms are 52 and 148 respectively.
