Question 9

A mixture of 50 kg of cement and gravel contains 10% of gravel. How many kg of gravel must be added to make the gravel content 28% in the new mixture?

Solution

Quantity of gravel in 50 kg mixture = $$\frac{10}{100}\times50=5$$ kg

Let $$x$$ kg of gravel must be added in the mixture,

=> $$(x+5)=\frac{28}{100}\times(x+50)$$

=> $$100x+500=28x+1400$$

=> $$100x-28x=1400-500$$

=> $$72x=900$$

=> $$x=\frac{900}{72}=12.5$$

$$\therefore$$ 12.5 kg of gravel must be added to make the gravel content 28% in the new mixture.

=> Ans - (C)

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