Question

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

Answer 1

Answer:

Given:

a=3

d=a2-a1 => 8-3

so, d=5

n=78

To find = a78.

solution:

an = a+(n-1)×d

a78 = 3+(78-1)×5

a78 = 3+77×5

a78 = 3+ 385

a78 = 388.

So the 78th term of this A.P.= 388.

Hope it will help you.

Answer 2

Answer:

16th term is 78

Step-by-step explanation:

1st term = a = 3

common difference = d = 8-3 = 5

nth term = a + (n-1)×d = 3 + (n-1)×5 = 78

=> (n-1)×5 = 78-3 = 75

=> n-1 = 75/5 = 15

=> n = 15+1 = 16