Answer:
Step-by-step explanation:
Formula

Where
change in value = Final value - initial value.
First find out the percentage of sales incresre from $5,000 to $10,000.
As given
Last year, sales at a book store increased from $5,000 to $10,000.
Final value = $10000
initial value = $5000
change in value = $10000 - $5000
=$5000
Put in the formula

Percentage = 100%
Sales increased 100% last year, from $5,000 to $10,000.
Second find out the percentage of sale decrease to $5,000 from $10,000.
As given
This year, sales decreased to $5,000 from $10,000.
Final value = $5000
Initial value = $10000
Change in value = $5000 - $10000
= - $5000
(This negative sign shows the decrease percentage.)
Put in the formula


Decrease Percentage = 50%
When sales dropped from $10,000 to $5,000 this year, sales decreased 50% .