Answer:
The 9th number is 28.
Step-by-step explanation:
Represent the common difference by d and the first term by f.
We can then write a formula for the nth term of this arithmetic sequence as follows;
a(n) = f+d(n-1)
We are told that the fifth term is 16; therefore, a(5) = 4+d(5-1) = 16. We need to solve this equation for d.
Performing the indicated multiplication: 4 + 4d = 16.
Subtracting 4 from both sides: 4d = 12
Isolating d by dividing both sides by 4: d = 3
Then the general formula for this sequence is a(n) = 4 + 3(n-1).
The 9th number in this sequence is thus a(9) = 4 + 3(9-1), or
a(9) = 4 + 3(8) = 28
