Question

Which term of an AP is 5,9,13,17,...81

Answer 1

a = 5

d = T2 - T1 = 9 - 5 = 4


L = a + ( n -1)] d

=> 81 = 5 + (n-1) 4

=> 76 = (n-1)4

=> n-1 = 19

=> n = 20

20th term of the give AP is 81

Answer 2

plz refer to this attachment