A company intoduces a special packing of mixed fruit juice with `20%` extra juice at no extra cost. If the special pack contains 660mL of juice, find the content of the standard pack.

Answer

To find the content of the standard pack of mixed fruit juice, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Problem**: We know that the special pack contains 20% extra juice compared to the standard pack. The special pack has a total of 660 mL of juice.

2. **Define the Standard Pack Volume**: Let the volume of the standard pack be \( x \) mL.

3. **Set Up the Equation**: Since the special pack contains 20% more juice than the standard pack, we can express this mathematically:
\[ \text{Standard Pack} + \text{20% of Standard Pack} = \text{Special Pack} \]
This can be written as:
\[ x + 0.2x = 660 \]
or equivalently,
\[ x + \frac{1}{5}x = 660 \]

4. **Combine Like Terms**: Combine the terms on the left side:
\[ \frac{5}{5}x + \frac{1}{5}x = 660 \]
This simplifies to:
\[ \frac{6}{5}x = 660 \]

5. **Solve for \( x \)**: To isolate \( x \), multiply both sides by \( \frac{5}{6} \):
\[ x = 660 \times \frac{5}{6} \]

6. **Calculate the Value**: Perform the multiplication:
\[ x = 660 \div 6 \times 5 = 110 \times 5 = 550 \]

7. **Conclusion**: Therefore, the content of the standard pack is:
\[ \boxed{550 \text{ mL}} \]