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WAEC Mathematics 2010 Paper

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Question : 32

Total: 49

If x km/h = y m/s, then y =

$\;\frac{7}{18}$ x
$\;\frac{11}{20}$ x
$\;\frac{4}{15}$ x
$\;\frac{5}{18}$ x

Solution:

Concept:

Convert speed from kilometres per hour to metres per second using standard unit relations.

Explanation:

Given:

x\ \mathrm{km/h} = y\ \mathrm{m/s}

.

We know

1\ \mathrm{km} = 1000\ \mathrm{m}

and

1\ \mathrm{h} = 3600\ \mathrm{s}

.

Rewrite

x\ \mathrm{km/h}

as

x \times \frac{1\ \mathrm{km}}{1\ \mathrm{h}}

.

Substitute the unit conversions:

x \times \frac{1000\ \mathrm{m}}{3600\ \mathrm{s}} = y\ \mathrm{m/s}

.

Simplify

\frac{1000}{3600}

to

\frac{5}{18}

.

So,

x \times \frac{5}{18}\ \mathrm{m/s} = y\ \mathrm{m/s}

.

Hence,

y = \frac{5}{18}x

.

Answer:

y = \frac{5}{18}x

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