WAEC 2023 Mathematics · Question 42

A notebook of length 15 cm was measured to be 16.8 cm, calculate, correct to two d.p, the percentage error in the measurement.

Options

A.12.00%
B.11.71%
C.10.71%
D.11.21%

Answer: A. 12.00%

Explanation written with AI and checked against the answer key

Analyze the question: The true length is 15 cm and the measured length is 16.8 cm. We need the percentage error, correct to 2 d.p. Concept: Error = |Measured value − True value| Percentage error = (Error ÷ True value) × 100% The usual WASSCE convention is to divide by the true (actual) value. Solution: Error = 16.8 − 15 = 1.8 cm Percentage error = (1.8 ÷ 15) × 100% = 0.12 × 100% = 12.00% Checking the other options: If you divided by the measured value instead, you would get (1.8 ÷ 16.8) × 100 = 10.71%. That is option C, a trap for students who divide by the wrong value. Options B and D do not come from any standard method. 12.00%. **Tip: Percentage error always uses the true/actual value as the denominator, unless the question says otherwise. Ask yourself: "What is the real value?" and divide by that.

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