Given an arithmetic progression 15 19 23 what number is in this sequence in 9th place?

In this arithmetic progression, the first term is a1 = 15.
Let’s find what is the difference of the given arithmetic progression:
d = 19 – 15 = 23 – 19 = 4.
The n-th member of the arithmetic progression is: an = a 1 + d * (n – 1).
It is required to find the 9th term of this arithmetic progression, that is, n = 9. We get:
a9 = 15 + 4 * (9 – 1),
a9 = 15 + 4 * 8,
a9 = 47.
Answer: 47.