### Video Transcript

The following figure shows two
thermometers that measure different temperatures. What is the difference in the
readings on the thermometers? Is it (A) 17 degrees Celsius, (B)
22 degrees Celsius, (C) 27 degrees Celsius, or (D) 31 degrees Celsius?

In this question, we’re asked to
determine the difference in the readings of two thermometers. Let’s notice first of all that the
thermometers have zero points in different positions. But they’re both reading the same
scale, that is, degrees Celsius. Therefore, the thermometer on the
left is only capable of measuring temperatures above the freezing point of water,
zero degrees C, while the thermometer on the right can measure temperatures below
this.

Now, if we read the temperature of
the thermometer on the left, we can see that it indicates a number that is one mark
lower than 20 degrees Celsius, which must mean it is measuring 19 degrees
Celsius. When we measure the temperature of
the thermometer on the right, we have to be a bit more careful, as the fluid in the
thermometer is indicating a negative temperature. This means that starting from the
negative five degrees Celsius mark, moving down one mark will indicate negative six
degrees Celsius, the number going up as the temperature goes down. Counting carefully, we see that the
thermometer on the right measures three marks down from negative five degrees
Celsius, indicating a temperature of negative eight degrees Celsius.

To find the temperature difference
now, we need to subtract the smaller measurement from the larger measurement. This means our difference will look
like 19 degrees C minus negative eight degrees C. Remember that when we subtract a
negative number, it’s the same as adding that positive number, 19 degrees C plus
eight degrees C. We can see then that this result is
equal to 27 degrees Celsius.

If we look at the readings and
double-check the difference between them, by counting from each of the two zero
points, we can see that the difference is indeed 27 degrees Celsius. So the correct answer to what is
the difference between these two thermometers is option (C), 27 degrees Celsius.