Atriangle has side lengths measuring 20cm, 5cm, and n cm. which describes the possible values of n?

The sum of any two sides must be greater than the third side.

So if n is the largest side:

n<20+5

n<25

And if 20 is the largest side:

n+5>20  subtract 5 from both sides

n>15

Since n>15 and n<25

15<n<25  or in interval notation:

n=(15, 25)