`4.5g` of an alloy of copper and zinc contains `3.5 g` of copper. How much copper will there be in `18.9 g` of alloy ?

Answer

To solve the problem step by step, we can follow these steps:

### Step 1: Understand the given information
We know that:
- 4.5 grams of the alloy contains 3.5 grams of copper.
- We need to find out how much copper is in 18.9 grams of the alloy.

### Step 2: Set up a proportion
We can set up a proportion based on the information given:
\[ \frac{3.5 \text{ g of copper}}{4.5 \text{ g of alloy}} = \frac{x \text{ g of copper}}{18.9 \text{ g of alloy}} \]
Where \( x \) is the amount of copper in 18.9 grams of alloy.

### Step 3: Cross-multiply
Cross-multiplying gives us:
\[ 3.5 \times 18.9 = 4.5 \times x \]

### Step 4: Calculate the left side
Now, we calculate \( 3.5 \times 18.9 \):
\[ 3.5 \times 18.9 = 66.15 \]

### Step 5: Set up the equation
Now we have:
\[ 66.15 = 4.5 \times x \]

### Step 6: Solve for \( x \)
To find \( x \), divide both sides by 4.5:
\[ x = \frac{66.15}{4.5} \]

### Step 7: Calculate \( x \)
Now we perform the division:
\[ x = 14.7 \]

### Conclusion
Thus, the amount of copper in 18.9 grams of the alloy is **14.7 grams**.

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