Final answer:
To find the percent decrease in the amount of money Callie earned babysitting, subtract the second amount from the first, divide it by the first amount, and multiply by 100.
Step-by-step explanation:
To find the percent decrease in the amount of money Callie earned babysitting, we need to calculate the difference between the two amounts and express it as a percentage of the original amount.
The original amount Callie earned was $20. The difference between the two amounts is $20 - $15 = $5. To express this as a percentage of the original amount, we divide the difference by the original amount and multiply by 100: $5 / $20 * 100 = 25%.
Therefore, the percent decrease in the amount of money Callie earned babysitting is 25%.