Question

Question 4 Which term of the A.P. 3, 8, 13, 18, … is 78?

Class 10 - Math - Arithmetic Progressions Page 106

Answer 1

let the term be "n"
as we know the first term is 3 and common difference is 5

78 = 3+ (n-1)5
15 = n-1
n=16

so the 16th term is 78

Answer 2

Let the term be ∅

Given first term = 3
and we can find the common difference as 8-3= 5

so, 78 = 3+ ( ∅ -1) 5

75 /5 = ∅ -1

15 +1 = 16 = ∅

there fore, 78 is the 16 term

hope helped!