Question

The sum of the 5th and 24th terms of an AP is 50. Find the sum of 1st and 28th terms? Find the sum of 1st 28 terms of this sequence

Answer 1

Hlw mate !!


Solution:

Given sum of 5th term and 9th term of AP=30

a+4d + a+8d =30

2a + 12 d = 30 ---equation (1)

Given that 25 term is three times of 3rd term in AP

25th term= 3 (8th term)

( a+ 24d)= 3(a +7d)

a+ 24d = 3a+ 21d
24d - 21 d= 3a- a
3d = 2a --- equation 2

Substitute the value of 2d in equation (1) we get

2a+ 12d = 30

3d +12d =30

15d =30

d = 2

2a = 3d
2a= 3x 2
2a= 6
a=3

THEREFORE AP is 3, 5,7, 9.


Hope it helpful