Problem
Example 4) Andrea and Phary are sharing a bag of popcorn at the movies. By himself, Phary can eat the whole bag of popcorn in $20 \mathrm{~min}$. Andrea takes $25 \mathrm{~min}$ to eat the whole bag. If they both eat popcorn at their usual rates, how quickly will they eat the popcorn?
Solution
Step 1 ：Find the combined rate of Andrea and Phary eating the popcorn: \(\frac{1}{20} + \frac{1}{25} = \frac{5}{100} + \frac{4}{100} = \frac{9}{100}\)
Step 2 ：Find the time it takes for them to eat the whole bag at this combined rate: \(\frac{1}{\frac{9}{100}} = \frac{100}{9} \approx 11.11\)
Step 3 ：\(\boxed{11.11}\) minutes
