The sequence 12, 15, 18, 21, 51, 81, ... consists of all positive multiples of 3 that contain at least one digit that is a 1. What is the 50th term of the sequence? (2006 National Target #5)

159

Step-by-step explanation:

Using the formula for arithmetic progression,

an = a + (n - 1) d

Where a is the first term

n is the number of terms or nothing term

d is the common difference.

From the question:

a = 12

d = 3

nth = 50

an = 12 + (50 - 1) 3

= 12 + (49) 3

= 12 + 147

= 159