Question

What is the probability that a randomly chosen two-digit positive integer is a multiple of 3.

Answer 1

Let n(s) = 90 

A = {12,15 ……………… 99} 

n(A) = 30

P(A) = \(\frac{n(A)}{n(S)}\) = \(\frac{30}{90}\) = \(\frac{1}{3}\)

Using a + (n — 1)d = T_n 

12+ (n – 1)³ = 99 

12 + 3x – 3 = 99 

3x = 99 – 9 

3x = 90; x = 30