Question

which term of the AP 5,9,13...is 81​

Answer 1

5,9,13........

$a = 5 \\ d = 4 \\ \\ l = a + (n - 1)d \\ 81 = 5 + (n - 1)4 \\ (n - 1)4 = 76 \\ n - 1 = \frac{76}{4} \\ n - 1 = 19 \\ n = 20$

So 20 th term is 81