Answer: 56.4102564% decrease
Explanation: First determine whether the number is increasing or decreasing. Since it changes from 39 to 17, it's going down so it's decreasing.
Now to find the percent decrease,
we divide the amount of change by the original number.
The amount of change is the difference between the two numbers
which in this case is 39 - 17 and the original number is 39.
39 - 17 is 22 so we're left with which gives us 56.4102564
Remember however that our problem is asking for a <em>percent</em>, not a decimal. So we need to write 56.4102564 as a percent by moving the decimal point 2 places to the right to get 56.4102564.
So when a number changes from 39 to 17, it has decreased by 56.4102564%.