Answer:
0°C
Explanation:
If the reading on a thermometer is -20°C and the temperature rises by 20°C, we can find the new reading by adding the change in temperature to the original reading.
Change in temperature = 20°C (given)
New reading = Original reading + Change in temperature
New reading = (-20°C) + 20°C
New reading = 0°C
Therefore, the new reading on the thermometer will be 0°C.