Question

The explicit formula for the geometric sequence 3, 15, 75, 375,… is _______

(a) 2*6! * 3^n-1

(b) 3 * 5^n-1

(c) 3! * 8^n-1

(d) 7 * 4^n-1

This question was addressed to me in an interview.

Asked question is from Discrete Probability in section Discrete Probability of Discrete Mathematics

Answer 1

Right option is (b) 3 * 5^n-1

For explanation I would say: The initial term is 3 and each subsequent term is the product of its previous term, the common ratio is 5. Thus the formula generating this sequence is an = 3 * 5^n-1.