4.1 Calculating with Formulas and Functions
It is important to be able to figure out the unknown variable in a function if you know the others. This you do by taking out the unknown variable.
We will look at two examples of formulas where you can do a little different calculation depending on which variables you know:
This is a well known formula which you use to calculate speed.
v: speed (v comes from the word velocity.)
d: distance
t: time
The formula looks like this:
If you know the distance and the time, then it is not a problem to calculate the speed.
Example:
d = 240 km
t = 3 h
If you know the speed and the time, then it is not a problem to calculate the distance.
v = 70 km/h
t = 2.5 h
The variable that you don’t know is d (the distance). How do you calculate the distance?
We begin by taking out the distance from the formula:

d · t 

v · t = 

We multiply both sides with t. 

t


d = v · t
Then we get:
d = 70 · 2.5
d = 175 km
