What is
as a decimal rounded to 3 decimal places?

“Three decimal places” is the same as “the nearest thousandth.” So, for example, if you are asked to round 3.264 to two decimal places it means the same as if your are asked to round 3.264 to the nearest hundredth. Some questions, like the example below, will ask you to “show your answer correct to two decimal places."

In this problem it decreased 20%

The answers are 20,30,80,180,960,890,1230,4560. on the first row