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
If the ratio of the sum of the first n terms of two A.Ps is (7n + 1) : (4n + 27), then find the ratio of their 9th terms.
Find the sum of all natural numbers between 1 and 100, which are divisible by 3.
Show that the sum of all odd integers between 1 and 1000 which are divisible by 3 is 83667.
If numbers n – 2, 4n – 1 and 5n + 2 are in A.P., find the value of n and its next two terms.
Which term of the AP 3,8, 13,18,…. Will be 55 more than its 20th term?
The 7th term of the an AP is -4 and its 13th term is -16. Find the AP.
Simplify `sqrt(50)`
If Sr denotes the sum of the first r terms of an A.P. Then , S3n: (S2n − Sn) is
If the second term and the fourth term of an A.P. are 12 and 20 respectively, then find the sum of first 25 terms:
Read the following passage:
|
India is competitive manufacturing location due to the low cost of manpower and strong technical and engineering capabilities contributing to higher quality production runs. The production of TV sets in a factory increases uniformly by a fixed number every year. It produced 16000 sets in 6th year and 22600 in 9th year. |
- In which year, the production is 29,200 sets?
- Find the production in the 8th year.
OR
Find the production in first 3 years. - Find the difference of the production in 7th year and 4th year.
