Amy had homework for math, science, and history. she spent 1/3 of her time working on math and 1/4 of her time working on science.

First we need to multiply to make the fractions have equal denominators so we can add/subtract.

math: 1/3 x 4/4=4/12
science: 1/4 x 3/3=3/12

Now we can find the time she spent on history (I assume this is what you are looking for)

Total time-math time-science time=history time
12/12-4/12-3/12
=5/12

Amy spent 5/12 of her time working on history.

So,

I will be assuming the same thing as the other user.

First, we have to convert the fractions so that they have common denominators.





Now we add the fractions together.



Now, to find the fraction of the time that Amy spent on history, we need to subtract the sum of the time she spent in math and science from one whole.



Amy spent 5/12 of her time working on history.