4. Which term of the AP:3, 8, 13, 18, ..., is 78?

Step-by-step explanation:

The first term of the AP (a) = 3

and common difference (d) = 8-3 = 5

therefore, a + (n-1) d = 78

=> 3 + (n-1) 5 = 78

=> n-1=75/5

=> n-1 = 15

=> n = 16

16th term of the AP is 78