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WAEC Mathematics 2011 Paper

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Question : 15

Total: 47

The length of a piece of stick is 1.75m. A girl measured it as 1.80m. Find the percentage error

$\frac{28}{7}$ %
$\frac{29}{7}$ %
5%
$\frac{20}{7}$ %

Solution:

Concept:

Percentage error compares the size of the error to the true value, expressed as a percentage.

Explanation:

True length of the stick

= 1.75\ \text{m}

.

Measured length

= 1.80\ \text{m}

.

Error

= 1.80 - 1.75 = 0.05\ \text{m}

.

Use the formula:

Percentage error

= \dfrac{\text{Error}}{\text{True value}} \times 100\%

Percentage error

= \dfrac{0.05}{1.75} \times 100\%

Simplify:

\dfrac{5}{175} \times 100 = \dfrac{100}{35} = \dfrac{20}{7}\%

Thus, the percentage error is

\dfrac{20}{7}\%

.

Answer:

D.

\dfrac{20}{7}\%

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