Problem
Jess puts 2 yellow counters and 1 blue counter in a bag. She then puts more blue counters in the bag. She is going to take one counter without looking. The probability that the counter will be blue is $\frac{4}{5}$. How many more blue counters did Jess put in the bag?
Solution
Step 1 ：Set up the equation: \(\frac{1 + x}{3 + x} = \frac{4}{5}\)
Step 2 ：Solve for x: \(x = 7\)
Step 3 ：\(\boxed{7}\) more blue counters were added
