Multiplying integers word problem
About this video
Snow melts at 2 centimetres per hour, and decreases are recorded as negative numbers, so the rate is -2 cm per hour. Multiplying -2 by 5 hours gives -10 cm: the snow depth fell by 10 centimetres.
You'll be able to
- use a negative number to represent a decrease in a word problem.
- multiply a negative rate by a positive time to find a total change.
- explain why a negative times a positive gives a negative.
Key words
- rate
- How much something changes for each unit of time, like 2 centimetres per hour.
- total change
- How much a quantity went up or down overall; negative means it went down.
Transcript
- [Instructor] After a winter storm, the snow on Windsor Street started melting at a rate of two centimeters per hour. Increases in snow levels are recorded with positive numbers. Decreases in snow levels are recorded with negative numbers. What was the total change in depth of the snow on Windsor Street after five hours?
Pause this video and try to figure this out. All right, so we know we're melting at a rate of two centimeters per hour. So we are melting. So this is a decrease in snow levels. So we're gonna record that with negative numbers. So our rate is negative two centimeters per hour and now how many hours is that going on for?
Well, we see it right there, five hours. So we're going to multiply that times five hours and what do we now get? Well, two times five is 10, but this is negative two times five. One way to think about it, if we have different signs, this is going to be negative.
Why does that make sense? Well, we keep taking two away for five hours, two centimeters away per hour for five hours so it makes sense that our total change after five hours is that we have lost 10 centimeters. This negative symbolizes that we have a decrease of 10 centimeters of our snow depth.
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