Calculate the quantity of pure gold in 100 g of an alloy of gold and copper.The densitites of gold, copper and the alloy are 19.9 g / cc ,9 g / cc and 16 g / cc respectively.

** let the quantity of gold be x.**

**therefore, quatity of copper be 100 - x.**

**now,**

**density = mass/volume**

**therefore density of gold = 19.9 = x /v1**

**density of coper = 9 = (100 - x)/v2**

**density of alloy = 16 = 100/(v1 + v2) .... {since volume occupied by both will be equal to the volume occupied by the alloy}**

**therefore,**

**16( x/19.9 + 100/9 - x/9) = 100**

**therefore,**

**16(x/19.9 - x/9) = 100 - 1600/9**

**therefore,**

**16(19.9x - 9x)/19.9 x 9 = 700/9**

**therefore, 10.9x = 700 x 19.9 /16**

**=> x = 700 x 19.9/10.9 x 16**

**therefore,**

**x = 79.8 g**

**therefore,**

**quantity of gold is approximately 80g .**

**hope it helps!!**

**cheers!!!**

**thumbs up plz...**

**
**