Advertisements
Advertisements
Question
Find the sum of first 20 terms of the following A.P. : 1, 4, 7, 10, ........
Advertisements
Solution
Let a be the first term and d be the common difference of the given A.P. Then, we have a = 1 and d = 3.
We have to find the sum of 20 terms of the given A.P.
Putting a = 1, d = 3, n = 20 in
`S_n = \frac{n}{ 2 } [2a + (n - 1) d]`
∴ `S_20 = \frac {20}{2} [2 × 1 + (20 - 1) × 3]`
= 10 (2 + 57)
= 10 × 59
= 590
APPEARS IN
RELATED QUESTIONS
The 19th term of an AP is equal to 3 times its 6th term. If its 9th term is 19, find the AP.
If (3y – 1), (3y + 5) and (5y + 1) are three consecutive terms of an AP then find the value of y.
The 9th term of an A.P. is equal to 6 times its second term. If its 5th term is 22, find the A.P.
Find the sum of n terms of the series \[\left( 4 - \frac{1}{n} \right) + \left( 4 - \frac{2}{n} \right) + \left( 4 - \frac{3}{n} \right) + . . . . . . . . . .\]
Q.10
Q.12
In a ‘Mahila Bachat Gat’, Sharvari invested ₹ 2 on first day, ₹ 4 on second day and ₹ 6 on third day. If she saves like this, then what would be her total savings in the month of February 2010?
If the nth term of an AP is (2n +1), then the sum of its first three terms is ______.
The first term of an AP of consecutive integers is p2 + 1. The sum of 2p + 1 terms of this AP is ______.
If sum of first 6 terms of an AP is 36 and that of the first 16 terms is 256, find the sum of first 10 terms.
