Question -
Answer -
Let the series be 7, A1,A2, A3, …….., An, 71
We know total terms inAP are n + 2
So 71 is the (n + 2)thterm
By using the formula,
An = a+ (n – 1)d
An =71, n = 6
A6 = a+ (6 – 1)d
a + 5d = 27 (5th term)
d = 4
so,
71 = (n + 2)th term
71 = a + (n + 2 – 1)d
71 = 7 + n(4)
n = 15
∴ There are 15 terms inAP