Question Video: Writing a Numerical Expression Involving Rational Numbers Then Evaluating It Mathematics • 7th Grade

The current temperature in a town is −5°F. An hour later, it dropped by 10° and 2 hours later, it rose by 7°. Write an expression to describe this situation, and then solve it to find the final temperature.

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Video Transcript

The current temperature in a town is negative five degrees Fahrenheit. An hour later, it dropped by 10 degrees. And two hours later, it rose by seven degrees. Write an expression to describe this situation and then solve it to find the final temperature.

Let’s first look at these numbers on a number line. So here, we have a number line. As we go to the right, the numbers increasing become larger and as we go to the left, the numbers become smaller, more negative.

So we know that the current temperature in a town is negative five degrees Fahrenheit. And then, one hour later, it dropped by 10 degrees. So we need to subtract 10, become more negative. So we should go left down the number line 10 degrees: one, two, three, four, five, six, seven, eight, nine, and ten. So we’re at negative 15 degrees.

Now, two hours later, it rose by seven degrees. We need to increase the temperature by seven degrees. So we need to move to the right seven: one, two, three, four, five, six, seven. Now, we’re at negative eight degrees. So this means negative eight degrees Fahrenheit would be our final temperature.

So the question asks us to write an expression to describe this situation. So we begin with negative five degrees and then it dropped 10 degrees. So we needed to add negative 10 degrees. But then, it rose by seven. So we will need to add seven. So this would be an expression. An expression does not have an equal sign.

Next, we’re supposed to solve for the final temperature and we did. We went from negative five degrees then dropped 10 degrees. And we were at negative 15 degrees. And then two hours later, we rose seven degrees. So we ended up at negative eight degrees Fahrenheit. Therefore, this will be our final answer.

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