Question 902222
at sea level the boiling point is 100 degrees centigrade.
at 5km above sea level, the boiling point of water is 82.5 degrees centigrade.


let x = the number of km above sea level.


when x = 0, the boiling point is 100 degrees centigrade.


when x = 5 km, the boiling point is 82.5 degrees centigrade.


the average change in boiling point is equal to (82.5 - 100) / 5 which is equal to -17.5 / 5 which is equal to -3.5 degrees centigrade per kilometer.


the formula becomes:


y = -3.5*x + 100


when x = 0, y = 100
when x = 5, y = 5*-3.5 = -17.5 + 100 = 82.5 degrees centigrade.


the graph looks like this:


<img src = "http://theo.x10hosting.com/2014/091602.jpg" alt="$$$" </>


the slope of the line becomes the change in the value of y divided by the change in the value of x.


the change in the value of y is the change in the boiling point of water.
the change in the value of x is the change in the number of kilometers above sea level.