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?
Quantity of gravel in 50 kg mixture = $$\frac{10}{100}\times50=5$$ kg
Let $$x$$Â kg of gravel must be added in the mixture,
=> $$(x+5)=\frac{28}{100}\times(x+50)$$
=> $$100x+500=28x+1400$$
=> $$100x-28x=1400-500$$
=> $$72x=900$$
=> $$x=\frac{900}{72}=12.5$$
$$\therefore$$Â 12.5Â kg of gravel must be added to make the gravel content 28% in the new mixture.
=> Ans - (C)
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