4/5
You don't need much skill to solve this. Lowest Term(s) mean "simplify". So make 20/25 as the simplest you can. Now, to do this, we must check if the number can be simplified.
This is by using the numbers: 2, 3, 4, 5, 6,... etc.
Let's use 2. It doesn't work. 3? No. 4? No. 5? YES!!
5 does work. Since 20/5 is 4. And 25/5 is 5!
This means that it's technically: (20/5)/(25/5)
And hopefully, you get 4/5 as your answer.