9.5.3 Changing Formulas

The same technique can be used to change formulas. For example, earlier in the unit, you found a formula to convert dollars into euros:

number of euros equals number of dollars multiplication 0.74

However, what if you were from Europe and wished to convert euros into dollars, say while you were shopping on vacation?

Then you would need a formula for the number of dollars based on the number of euros. We can tackle this by drawing the “doing and undoing” diagrams for this situation:

So, starting at the right of the undoing diagram, the formula for converting euros into dollars is:

number of dollars equals number of euros division 0.74

Activity Symbol Activity: Miles and Kilometers

To change kilometers into miles, you used the formula:

distance in miles equals distance in kilometers multiplication 0.6214

Starting with “distance in kilometers,” draw a doing diagram to get the distance in miles. Draw the undoing diagram and write down the formula for changing miles into kilometers.

Your formula should start “distance in kilometers =.”

Answer Symbol


The doing and undoing diagrams are shown below.

So, the formula for converting miles into kilometers is:

distance in kilometers equals distance in miles division 0.6214

9.5.2 Doing and Undoing

9.5.4 How Many Minutes for Chatting?