You exercise for 3/4 of an hour. you jump rope for 1/3 of that time. in simplest form, what fraction of the hour do you spend jumping rope?

The answer is 1/4 of the hour

Explanation:
The word "of" in fraction word problems most usually means to multiply. So, you take 3/4 and multiply by 1/3. 3/4 x 1/3 = 3/12 and you can simplify it to 1/4.

Well what you do is you have to multiply 3/4 and 1/3 which would look like this 

3            1          3  
--    X    ---  =      and then you simplify which would be 1/4 of the hour. 
4            3         12 
hope that helped