Advertisements
Advertisements
Question
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?
Advertisements
Solution
First term, a = 8
Common difference, d = 9
Let the nth term be the last term.
∴ l = an = 350
⇒ a + (n − 1) d = 350
⇒ 8 + (n − 1) × 9 = 350
⇒ (n − 1) × 9 = 342
`rArr n-1=342/9=38`
`rArrn=38+1=39`
Thus, there are 39 terms in the given A.P.
Sum of 39 trems , `S_39=39/2(a+a_39)`
`=39/2xx(8+350)`
`=39/2xx358`
`=6981`
APPEARS IN
RELATED QUESTIONS
Find the sum of the first 22 terms of the A.P. : 8, 3, –2, ………
If the numbers (2n – 1), (3n+2) and (6n -1) are in AP, find the value of n and the numbers
Find the first term and common difference for the following A.P.:
5, 1, –3, –7, ...
The sum of first n terms of an A.P. is 3n2 + 4n. Find the 25th term of this A.P.
If S1 is the sum of an arithmetic progression of 'n' odd number of terms and S2 the sum of the terms of the series in odd places, then \[\frac{S_1}{S_2} =\]
In an AP. Sp = q, Sq = p and Sr denotes the sum of first r terms. Then, Sp+q is equal to
Q.4
How many terms of the A.P. 27, 24, 21, …, should be taken so that their sum is zero?
If an = 3 – 4n, show that a1, a2, a3,... form an AP. Also find S20.
If Sn denotes the sum of first n terms of an AP, prove that S12 = 3(S8 – S4)
