Video: Calculating Differences Between Negative Numbers

The freezing point of bromine is −7°C, while the freezing point of methane is −182°C. How much warmer is bromine’s freezing point than methane’s?

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Video Transcript

The freezing point of bromine is negative seven degrees Celsius, while the freezing point of methane is negative 182 degrees Celsius. How much warmer is bromine’s freezing point than methane’s?

As we want to calculate how much warmer the freezing point is, we know that our answer will be positive. We could do this using a number line. How can we get from negative 182 to negative seven? We could do this by calculating the difference between negative 182 and negative seven. Alternatively, we could see that we need to add 182 to get from negative 182 to zero. To get from zero back to negative seven, we need to subtract seven. This means that to get from negative 182 to negative seven, we need to add 182 and then subtract seven. 182 minus seven is equal to 175. This means that bromine’s freezing point is 175 degrees Celsius warmer than methane’s.

An alternative method here would be to subtract negative 182 from negative seven. We know that subtracting a negative number is the same as adding that number. Once again, negative seven plus 182 is equal to 175, confirming that our answer is correct.

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