Test 4 Section 3 #20 please. Also Mike, I still didn’t know how to answer the question even after I went and reviewed it from the official test breakdown section of your book.

There are a lot of words here, but when you strip that all away, this is basically a question about slope. You know you have a change in distance from the earth’s surface of 50 km to 80 km, and a change in temperature from –5° C to –80° C.

The big trick is that we’re told we need to find the degrees by which the temperature changes every 10 km, so we should think about our distance values in tens. That is, instead of 50 km and 80 km, we should use 5 and 8 and our units will be tens of km.

So let’s calculate the change in temperature in degrees Celsius per change in 10 km distance.

    \begin{align*}&\dfrac{\text{Change in Temperature in degrees Celsius}}{\text{Change in Distance in 10 kilometer units}}\\\\=&\dfrac{-5-(-80)}{5-8}\\\\=&\dfrac{75}{-3}\\\\=&-25\end{align*}

So there you go. Every 10 km further you go from the Earth’s surface, the temperature drops by 25° C.

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