Over the weekend, Ed spent 1 1/4 hours doing his math homework and 1 3/4 hours doing his science project. Altogether, how much time did Ed spend doing homework over the weekend?

You have to add 1 1/4 + 1 3/4. Since they have common denominators you can just add all the numbers, 1+1=2, 1+3=4 since 4/4 is equal to one, you would add a one to the 2, so the answer would be 3. So Ed spent 3 hours doing homework during the weekend.