Video: Solving Word Problems Involving Rates

If the temperature outside is −4℉ and it’s falling at a rate of 5 degrees per hour, what will the temperature be in 5 hours?

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Video Transcript

If the temperature outside is negative four degrees Fahrenheit and it’s falling at a rate of five degrees per hour, what will be the temperature in five hours?

So we’re beginning at a temperature of negative four degrees Fahrenheit. And the temperature is falling. So it is decreasing at a rate of five degrees per hour. So after one hour, we need to go down five degrees.

So if we were to imagine this on a number line, we’re beginning at negative four. And if we’re decreasing, we’re gonna become more negative. So we need to move left on the number line. And if we would move left five, we would be at negative nine. So after one hour, we would be at negative nine degrees Fahrenheit.

So if another hour went by and we went down five more degrees, we would be at negative 14. And after another hour of decreasing five degrees, we would be at negative 19 degrees Fahrenheit. So so far, three hours have went by. So we need to pass two more hours because we need the total of five hours.

So after another hour of decreasing five degrees, we would be at negative 24 degrees Fahrenheit. And finally, after one more hour, totaling five hours, we would decrease another five degrees and be at negative 29 degrees Fahrenheit. So if originally the temperature outside was negative four degrees and it fell at a rate of five degrees per hour, after five hours, it would be negative 29 degrees Fahrenheit.

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