Question

The number of elements in the set {n ∈ \(\mathbb{N}\) : 10 ≤ n ≤ 100 and 3ⁿ - 3 is a multiple of 7} is____

Answer 1

Correct answer is 15

n∈[10, 100] 

3ⁿ – 3 is multiple of 7 

3ⁿ = 7λ + 3 

n = 1, 7, 13, 20,……97

Number of possible values of n = 15