An alloy of gold and silver weight 50 g. It contains 80% gold. How much gold should be added to the alloy so that percentage of gold is increased to 90 ?
A. 30 g
B. 40 g
C. 50 g
D. 60 g
Answer: Option C
Solution(By Examveda Team)
Quantity of gold in the alloy := 80% of 50 g
= $$\left( {\frac{{80}}{{100}} \times 50} \right)$$ g
= 40 g
Let x g of gold be added
Then,
$$\eqalign{ & \Rightarrow \frac{{40 + x}}{{50 + x}} = \frac{{90}}{{100}} \cr & \Rightarrow \frac{{40 + x}}{{50 + x}} = \frac{9}{{10}} \cr & \Rightarrow 400 + 10x = 450 + 9x \cr & \Rightarrow x = 50 \cr} $$
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