Answer:
$20
Step-by-step explanation:
We are given the percentages of how much she spent on each purchase but we need the percentage of what is left after each purchase. We calculate this by subtracting each percentage from 100% like so.
100% - 40% = 60%
100% - 20% = 80%
100% - 50% = 50%
Next we need to do is change the percentages into decimal format. We do this by moving the decimal 2 digits to the left. Therefore the percentages wasted are the following
60.0% ⇔ 0.60
80.0% ⇔ 0.80
50.0% ⇔ 0.50
Now that we have the percentages in decimal format we can calculate the total price (t) by retracing the spending process. The spending process was following.
So we have to retrace by solving for , then
, and finally (t)
... divide both sides by 0.50
.... divide both sides by 0.20
.... divide both sides by 0.60
Finally we can see that the Total amount of money that Alice had before lunch was $20