Question

which term of the A.P.3,8,13,18,...is 78?

Answer 1

Solution :

A.P : 3,8,13,18,..

a = 3 , d = 8-3 = 5

An = 78

a+(n-1)d = 78

3+(n-1)5 = 78

(n-1)5 = 78-3

(n-1)5 = 75

(n-1) = 75/5

(n-1) = 15

n = 15+1

=> n = 16

Hence 78 is the 16 th term of Given AP.

Answer 2

Heya friend,

Here is your answer,

Since the following sequence is in AP,
Therefore,

First term (a) = 3
Common difference (d) = 8 - 3 = 5
Tn = 78

Now, applying the formula for AP,

Tn = a + (n - 1)×d

=> 78 = 3 + (n - 1)×5

=> 75 = 5n - 5

=> 80 = 5n

=> n = 80/5

=> n = 16 (ans)

Therefore, 16th term of this AP will be 78.


Hope it helps you.
Thank you.