Teachers at Price Middle School are planning a birthday party for the principal. Planners estimated that 42 slices of cake would be needed. In fact, only 30 slices of cake were eaten. What was the percent error in the estimate of how much cake was eaten? A student solved the problem and showed his work below. What was his error?

StartFraction StartAbsoluteValue 42 minus 30 EndAbsoluteValue over 42 EndFraction(100) Almost-equals 6%
The planners did not use the absolute error in the ratio.
The planners compared the absolute error to the approximate value.
The planners did not multiply by 100 to get the percent.
The planners divided incorrectly and got the wrong answer.