Q70 of 84 Page 5

The sum of 5th and 9th terms of an AP is 30. If its 25th term is three times its 8th term, find the AP. (CBSE 2014)

a5 +a9=30

(a +4d) + (a +8d)=30


2a +12d=30


a + 6d=15 (i)


Acc. To question,


a25 =3a8


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


3d=2a


3d=2(15 -6d) [from(i)]


15d=30


d=2


Putting the value of d in (i),


a= 15 – 6(2)=3


a1 = a=3


a2 =a +d=3 +2=5


a3 =a +2d=3 + 2(2)=7


Hence, the A.P. is

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