If the outside temperature drops by 10 degrees Centigrade, how many degrees does it drop in Fahrenheit?

To convert a temperature change from Celsius to Fahrenheit, you can use the formula for the conversion of temperature differences:

[ \Delta F = \Delta C \times \frac{9}{5} ]

In this case, the temperature drop is 10 degrees Celsius. Plugging this into the formula gives:

[ \Delta F = 10 \times \frac{9}{5} = 10 \times 1.8 = 18 ]

This calculation shows that a 10-degree decrease in Celsius corresponds to an 18-degree decrease in Fahrenheit. Hence, the correct choice correctly reflects the conversion of a 10-degree drop in Celsius to the equivalent drop in Fahrenheit, which is 18 degrees.