Advertisements
Advertisements
प्रश्न
The sum of first 20 odd natural numbers is
विकल्प
100
210
400
420
उत्तर
Let a be the first term and d be the common difference.
We know that, sum of first n terms = Sn = \[\frac{n}{2}\][2a + (n − 1)d]
The given series is 1 + 3 + 5 + ......
First term = a = 1.
Common difference = d = 3 − 1 = 2
∴ S20 = \[\frac{20}{2}\] 2 × 1 + (20 − 1)2]
= 10(2 + 19 × 2)
= 10(40)
= 400
APPEARS IN
संबंधित प्रश्न
In an A.P., if S5 + S7 = 167 and S10=235, then find the A.P., where Sn denotes the sum of its first n terms.
The sum of the first p, q, r terms of an A.P. are a, b, c respectively. Show that `\frac { a }{ p } (q – r) + \frac { b }{ q } (r – p) + \frac { c }{ r } (p – q) = 0`
In an AP: Given a = 5, d = 3, an = 50, find n and Sn.
If the pth term of an A. P. is `1/q` and qth term is `1/p`, prove that the sum of first pq terms of the A. P. is `((pq+1)/2)`.
Find the sum of the following arithmetic progressions:
41, 36, 31, ... to 12 terms
If (2p – 1), 7, 3p are in AP, find the value of p.
If the first term of an A.P. is 2 and common difference is 4, then the sum of its 40 terms is
The common difference of the A.P.
If k, 2k − 1 and 2k + 1 are three consecutive terms of an A.P., the value of k is
Find the sum of first seven numbers which are multiples of 2 as well as of 9.
