Question Video: Subtracting Integers in Word Problems Involving Temperature

On a certain day, the high temperature was 64°F, and the low temperature was 55°F. Mason thought the change in the temperature on that day was 9°F, and Chloe thought it was 119°F. Who is correct?

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Video Transcript

On a certain day, the high temperature was 64 degrees Fahrenheit, and the low temperature was 55 degrees Fahrenheit. Mason thought the change in the temperature on that day was nine degrees Fahrenheit, and Chloe thought it was 119 degrees Fahrenheit. Who is correct?

To recognise which one of these two children is correct? We need to understand what the question is asking us. We can use a bar model to help us do this. Now because we’re talking about temperature and thermometers show temperature vertically, let’s make our bars vertical bars. We’re told that on a certain day, the high temperature was 64 degrees Fahrenheit. So let’s use this bar to represent that temperature. We’re then told that the low temperature on the same day was 55 degrees Fahrenheit. Let’s let the pink bar represent this. Now, the important phrase in this problem are the words “change in the temperature”.

Mason thought the change in the temperature was nine degrees, and Chloe thought it was 119 degrees. But where can we see the change in temperature on our bar model? The change in temperature is seen when we go from the highest temperature down to the lowest temperature. In other words, it’s this distance here. It’s the difference between 64 and 55. And we can find the difference by using subtraction, finding 55 less than 64. Now, if we look at both Mason and Chloe’s ideas, we can see that Mason is correct. Chloe’s answer is larger than 64 not less than it. Looks like she may have added the two numbers together.

But just to check that Mason’s correct, let’s find the difference between 55 and 64. Because these numbers are so close together, we could start at 55 and count up. See how much we have to add on to get to 64. We know that 55 plus 10 would take us to 65. So we need to subtract one off that to take us to 64. Instead of adding 10, we’d need to add nine. The difference between 64 and 55 then must be nine. And so, the difference between the two temperatures is nine degrees.

The difference between a high temperature of 64 degrees Fahrenheit and a low temperature of 55 degrees Fahrenheit can be found by finding the difference between these two numbers or using subtraction. 64 take away 55 equals nine. And so, the child whose idea is correct is the one that thought the change in temperature on that day was nine degrees Fahrenheit. And that child was Mason.

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