Question: Which term of the AP: 3, 8, 13, 18, …., is 78?
Explanatory Answer
The given AP is 3, 8, 13, .....
a = 3, d = 5, an = 78
an = a + (n – 1) d
78 = 3 + (n – 1) 5
75 = (n – 1) 5
n – 1 = 15
n = 16
The 16th term of the AP is 78.