A relationship that states that two ratios or two rates are equal.
If \(10\) beans have a mass of \(17\text{ g}\), then \(30\) beans have a mass of \(51\text{ g}\).
Thus, the proportion is,
\(\dfrac{17\text{ g}}{10\text{ beans}}=\dfrac{51\text{ g}}{30\text{ beans}}.\)
The electricity costs \(43.6\text{ sen}\) for \(2\text { kilowatt-hour (kWh)}\).
How much does \(30\text{ kWh}\) cost?
i) Unitary method
The cost of electricity for \(2\text{ kWh}\) is \(43.6\text{ sen}\).
So, the cost of electricity for \(1\text{ kWh}\) is
\(\begin{aligned}&=\dfrac{43.6\text{ sen}}{2} \\\\&=21.8\text{ sen}. \end{aligned}\)
Thus, the cost of electricity for \(30\text{ kWh}\) is
\(\begin{aligned}&=30\times21.8 \\\\&=654\text{ sen}. \end{aligned}\)
ii) Proportion method
Let the cost of electricity for \(30\text{ kWh}\) be \(x\text{ sen}\).
\(\begin{aligned} \dfrac{43.6\text{ sen}}{2\text{ kWh}}&=\dfrac{x\text{ sen}}{30 \text{ kWh}} \end{aligned}\)
We can see that
\(2\text{ kWh}\times15=30\text{ kWh}.\)
Thus,
\(\begin{aligned}x&=43.6\times15 \\\\&=654. \end{aligned}\)
iii) Cross multiplication method
\(\begin{aligned}\dfrac{43.6}{2}&=\dfrac{x}{30} \\\\2\times x&=43.6\times30 \\\\x&=\dfrac{1\,308}{2} \\\\&=654. \end{aligned}\)
From these methods, the cost of electricity consumption for \(30\text{ kWh}\) is \(\text{RM}6.54\).
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