Question

Sally estimated that her call would take twenty-one minutes but it actually took fifteen minutes. What was her percent of error?

Answer 1

(21-15)/21 * 100.

Answer 2

28.5 %

Answer 3

it is 6/21 = 2/7 changed to a percent
2/7 * 100 = 28 4/7 % (as a mixed number) or 28.571428% repeating
you could round, if appropriate, to 28.6%