A student determined in the laboratory that the percent by mass of water in cus04 5h20 is 38.0% if the accepted value is 40% what is the percent of error

Percent error is [ (abs (experimental - actual)) / (actual) ] * 100

(38.0 - 40.0) / 40.0 = 2.0 / 40 = 0.05

0.05 * 100 = 5

since there are 2 sigfigs, the answer is 5.0 %

I made the 2 positive since the absolute value of 38.0 - 40.0 was taken

There are only 2 sigfigs because of the subtraction of 38.0 - 40.0 gives 2.0, only 2 sigfigs