Answer
The middle term is $13$.
Work Step by Step
With arithmetic sequences with three consecutive terms, the middle term can be found by taking the arithmetic mean of the two terms that are given. The arithmetic mean is given by the formula:
arithmetic mean = $\frac{x + y}{2}$
Substitute the values given into the formula:
arithmetic mean = $\frac{5 + 21}{2}$
Add to simplify:
arithmetic mean = $\frac{26}{2}$
Simplify the fraction:
arithmetic mean = $13$
The middle term is $13$.
