Math CentralQuandaries & Queries


Question from Carol, a student:

Zack is packing for a trip to Scotland. He read that the average
temperature in the Summer is 18degrees C during the day, and 7 degrees
during the night. What is the difference between the high and low
temperatures in degrees Fahrenheit? (F=9/5C=32)

Assuming the temperatures that are given below are both in degrees
Celsius, the difference in degrees celsius (high minus low) is 18 - 7 = 11
degrees Celsius.

This is a good time to use ratios. Using a standard metric conversion chart
each degree difference in Celsius is 9/5 of a degree in Fahrenheit. Thus
we need to solve the proportion:

11:x = 1:9/5

Treating them like fractions we have x/11 = 9/5. Cross multiplication gives
x = 11 x 9/5 = 99/5 = 19 4/5 degrees.

L. Dame

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