Advertisements
Advertisements
Question
If the first term of an A.P. is 5, the last term is 15 and the sum of first n terms is 30, then find the value of n.
Advertisements
Solution
a = 5
Tn = l = 15
Sn = 30
n = ?
Sn = `n/2(a + l)`
⇒ 30 = `n/2(5 + 15)`
⇒ 60 = n × 20
⇒ 3 = n
APPEARS IN
RELATED QUESTIONS
How many terms of the A.P. 18, 16, 14, .... be taken so that their sum is zero?
Find four numbers in A.P. whose sum is 20 and the sum of whose squares is 120
In an AP: Given a = 5, d = 3, an = 50, find n and Sn.
A small terrace at a football field comprises 15 steps, each of which is 50 m long and built of solid concrete. Each step has a rise of `1/4` m and a tread of `1/2` m (See figure). Calculate the total volume of concrete required to build the terrace.
[Hint: Volume of concrete required to build the first step = `1/4 xx 1/2 xx 50 m^3`]
Find the sum to n term of the A.P. 5, 2, −1, −4, −7, ...,
Find the sum of all even integers between 101 and 999.
If `4/5 `, a, 2 are in AP, find the value of a.
Shubhankar invested in a national savings certificate scheme. In the first year he invested ₹ 500, in the second year ₹ 700, in the third year ₹ 900 and so on. Find the total amount that he invested in 12 years
The sum of first n terms of the series a, 3a, 5a, …….. is ______.
An AP consists of 37 terms. The sum of the three middle most terms is 225 and the sum of the last three is 429. Find the AP.
