Question

The ratio of zinc and copper in an alloy is $7:9$$.$ If the weight of copper in the alloy is $11.7$ kg$,$find the weight of zinc in the alloy$.$

Answer 1

Step $1:$ To find the weight of zinc in the alloy.

Given, Ratio of zinc and copper in an alloy $=$$7:9$

Weight of copper $=$$11.7$ kg

Sum of the terms of the ratio $=7+9$

$=16$

Step 2$:$ Now find the weight of copper in the alloy

Let x kg of zinc is mixed in the alloy

Total mixture $=\left(x+11.7\right)$ kg

Share of copper in the alloy $=\frac{9}{16}\times \left(x+11.7\right)$

But pure copper in the alloy $=11.7$ kg

$\frac{9}{16}\times \left(x+11.7\right)$$=11.7$

$\left(x+11.7\right)=\frac{16\times 11.7}{9}$

$\left(x+11.7\right)=16\times 1.3$

$\left(x+11.7\right)=20.8$

$x=20.8-11.7$

$x=9.1$

Hence, amount of zinc in the alloy is $9.1$ kg