Gold is 19 times as heavy as water and copper 9 times as heavy as water. The ratio in which these two metals be mixed so that the mixture is 15 times as heavy as water is: Options:
A) 1 : 2  B) 2 : 3  C) 3 : 2  D) 19: 135  E) None of these
Explanation:   This question can be solved using weighted average formula. If two quantities of weights m, n have concentrations x, y are mixed then, final concentration = mx+ny/m+n   Take 1 unit of gold and x units of copper.   1×19+x×9/1+x=15⇒19+9x=15+15x   ⇒x=2/3   So they are to be mixed in the ratio 1 : x = 1:2/3 or 3 : 2   3 : 2orrect Option: 3 : 2
<result>C</result>
Gold is 19 times as heavy as water and copper 9 times as heavy as water. The ratio in which these two metals be mixed so that the mixture is 15 times as heavy as water is: