Question

In the series 3, 9, 15, ...... what will be the 21st term?
A.117
B.121
C.123
D.129

Answer 1

here is your answer

by using formula,

An = a+(n-1)d

An = ?
a = first term = 3
n = 21
d = difference between two consecutive numbers = 6

now,

solution :

An = a+(n-1)d
An = 3+(21-1)6
An = 3+120
An = 123

so, the 21st term is 123.

Answer 2

Hello!!

a = 3

d = 9 - 3 = 6

a21 = 3 + 20 × 6

= 3 + 120

= 123

Thanks!❤