Question

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An ore contains 5% copper. How much ore is required to obtain 400 g of copper?

(a) 2 kg
(b) 4 kg
(c) 6 kg
(d) 8 kg

Answer 1

(d) 8 kg
Let x kg be the required amount of ore.
Then, 5% of x kg = 400 g = 0.4 kg [∵ 1 kg = 1000 g]
⇒ $\left(\frac{5}{100}\times x\right)=0.4$
⇒ x = $\left(\frac{0.4\times 100}{5}\right)$ = 8
Hence, 8 kg of ore is required to obtain 400 g of copper.