Mary and Ann are going sledding. Mary slides down a hill that's 630 feet long at a speed of 90 feet/minute. Ann slides down a hill that's 800 feet long at a rate of 40 feet/minute. How much longer does Ann's trip take than Mary?
First find the total time Mary's trip takes: 630 feet / 90 feet/minute = 
<gadget id="calculator">630/90</gadget>
<output>7</output>
7 minutes.
Then find the total time Ann's trip takes: 800 feet / 40 feet/minute = 
<gadget id="calculator">800/40</gadget>
<output>20</output>
20 minutes.
Then subtract Mary's time from Ann's time to find the difference: 20 minutes - 7 minutes = 
<gadget id="calculator">20-7</gadget>
<output>13</output>
13 minutes.

<result>13</result>