Asked by Umaru Monsurat

the first term of an arithmetic progression is 3 and the fifth term is is 9.find the number of terms in the progression if the last term is 81
Answered by Ms. Sue
Isn't your school subject math?

Answered by Steve
well, since

T5-T1 = 4d, d=3/2
we know a=3, so

Sn = n/2 (2*3+(n-1)(3/2))
3/4 (n^2+3n) = 81
n^2+3n-108 = 0
(n+12)(n-9) = 0
n=9

and the sequence is

3 4.5 6 7.5 9 10.5 12 13.5 15
The sum is 81
Answered by Anonymous
Thank you
Answered by Ayobami
It is math
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