Karen is planning writing assignments for her fifth grade class. She knows each short-answer question takes 3 minutes to answer, each paragraph takes 15 minutes to write, and each essay takes an hour to write. If Karen assigns 2 essays and 5 paragraphs, how many short-answer questions should she assign if she wants to assign 4 hours of homework total?
First figure out how many minutes 4 hours is: 4 hours * 60 minutes/hour = 
<gadget id="calculator">4*60</gadget>
<output>240</output>
240 minutes.
Then figure out how long the two essays will take by multiplying the time per essay by the number of essays: 2 essays * 1 hour/essay * 60 minutes/hour = 
<gadget id="calculator">2*1*60</gadget>
<output>120</output>
120 minutes.
Use the same method to find the total time spent writing paragraphs: 15 minutes/paragraph * 5 paragraphs = 
<gadget id="calculator">15*5</gadget>
<output>75</output>
75 minutes.
Now subtract the time spent on essays and paragraphs from the total time to find the time spent on all the short answer questions: 240 minutes - 120 minutes - 75 minutes = 
<gadget id="calculator">240-120-75</gadget>
<output>45</output>
45 minutes.
Finally, divide the total time spent on short-answer questions by the time per question to find the number of questions: 45 minutes / 3 minutes/question = 
<gadget id="calculator">45/3</gadget>
<output>15</output>
15 questions.

<result>15</result>