Question

50 g of an alloy of gold and silver contains 80% gold (by weight). The quantity of gold, that is to be mixed up with this alloy, so that it may contain 95% gold is 

(a) 200 g 

(b) 150 g 

(c) 50 g 

(d) 10 g

Answer 1

(b) 150 g

In 50 gm of an alloy of gold and silver, the quantity of gold = 40 gm and the quantity of silver = 10 gm,

Let x gm of gold be mixed in 50 gm of an alloy of gold and silver such that quantity of gold becomes 95%.

Then,  40 + x = 95% of (x + 50)

 40 + x = \(\frac{19}{20}\)( x+ 50)

\(\Rightarrow\) 800 + 20x = 19x + 950

\(\Rightarrow\) x = 150.