# Sterling silver is an alloy made by combining silver with copper in a ratio of 23 to 2. How much copper should be combined with 70 kg of silver to make sterling silver?

Dec 31, 2016

$2 C u \leftrightarrow 23 A g$. Question is ?Cuharr70Ag
A ratio question.

#### Explanation:

$2 \div 23 = X \div 70$ or $\frac{2}{23} = \frac{X}{70}$

Cross-multiply:
$23 X = 2 \cdot 70 \to X = \frac{2 \cdot 70}{23} \approx 6.09$ kg of copper.

Another way:

$70$kg amounts to $\frac{70}{23} = 3 , 0347. . .$ times as much as $27$

So we need $3 , 0347. . .$ times as much copper (same answer)