Anna is saving $6.35 a week to buy a computer game that costs $57.15. How many weeks will she have to save to buy the game?
Divide the total amount by the amount saved per week to find the number of weeks.
I have demonstrated where the shortcut method comes from!
There are shortcut methods that are used so much that they tend to be taken for granted. These shortcuts are based on first principle approaches but help you to skip a lot of stages.
To help understanding of what is going on with this I am going to use the first principles method.
We are given an initial condition of $6.35 saved in a week.
This can be expressed as
The ratio is fixed so we can equate initial condition directly to target condition.
Let the length of time to save the full amount in weeks be
The objective is to get
Dividing out gives: