Wednesday, March 4, 2009

Context for division by negative (If you find other examples, please share them by commenting on this entry.)

(1) My friend gave me 12 tickets and said I can owe her the money. The tickets are 4 for a $1. How much do I owe her for the 12 tickets? This could be solved by dividing 12 tickets by -4 to get -3, which means that I owe her $3.

(2) While scuba diving, it takes me 1/2 second to descend one foot. I was descending for 3 seconds. What is my change in depth? This could be solved by dividing 3 by -1/2 to get -6. Which means I have descended 6 feet.

(3) It is now 4pm. A few hours ago I had a dozen cookies. I have been eating the cookies at a constant rate of 4 cookies/hour. At what time did I start eating? This can be solved by dividing 12 by -4 to get -3. So 3 hours have gone by, which means I started eating the cookies at 1pm.

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