Every week a technician in a lab needs to test the scales in the lab to make sure that they are accurate. She uses a standard mass that is exactly 4g and gets the following 4.05g 3.98g and 4.021g which is the most precise

Precision is a measure of how close a value is to the ideal value. In this case, we calculate the difference to know what is the closest to 4 g:

4.05 - 4 = 0.05

3.98 - 4 = - 0.02

4.021 - 4 = 0.021

We can see that the value of 3.98g has the lowest difference and is therefore the closest to 4g. Hence the most precise is:

3.98 g