Question

if first term of an A.P is 3, common difference is 5 and nth number of an A.P is 78 the the value of n is​

Answer 1

Answer:

16th

Step-by-step explanation:

The given sequence is 3, 8, 13, 18, ....78.

'a' = 3, 'd' = 5, last term = 78, 'n' = ?

t

n

=a+(n−1)d

⟹78=3+(n−1)5

⟹78=3+5n−5

⟹78=5n−2

⟹5n=80orn=16.

The 16th term is 78.

Answer 2

Answer:

15

Step-by-step explanation:

Given,

a = 3

d = 5

aₙ = 78

To find : n

l = aₙ = 78

n = ( l - a ) / d

  = ( 78 - 3 ) / 5

  = 75 / 5

n = 15