Answer :
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)
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)