Question

A and B are two alloys of gold and copper prepared by mixing metals in the ratio 7: 2 and 7:11, respectively. If equal quantities of the alloys are melted to from a third alloy C the ratio of gold and copper in C will be

• A. 5:7
  
• B. 5:9
  
• C. 7 :5
  
• D. 9 :5
  
  
• E. None of these

Answer 1

The correct option is C 7 :5


Here, $a_1=7$
$b_1=2$
and $a_2=7$
$b_2=11$
By Short Trick 1
Ratio of gold and Copper in C
$=\frac{\frac{7}{9}+\frac{7}{18}}{\frac{2}{9}+\frac{11}{18}}$
$=\frac{14+7}{4+11}=\frac{21}{15}=7:5$