A student is using a graduated cylinder to measure the volume of water and reports a reading of 18 m

Percent error compares how far your measurement is from the true (accepted) value. The formula is: percent error = (|measured value − true value| ÷ true value) × 100. The true value here is the teacher’s reading, 18.4 mL, and the student’s measured value is 18 mL.

First find the error: |18 − 18.4| = 0.4 mL. Now divide by the true value: 0.4 ÷ 18.4 = 0.02174 (rounded). Multiply by 100: 0.02174 × 100 = 2.174%.

Rounded to two decimal places, the student’s percent error is 2.17%. A common mistake is dividing by the student’s own reading (0.4 ÷ 18 = 2.22%). Always divide by the accepted or true value, not by your own measurement.