Finding the Third Proportional to 128.50 and 221.50

Step by Step Solution

1. Step 1: Write the proportion equation
   128.50 : 221.50 = 221.50 : x
2. Step 2: Convert to fraction form
   128.50/221.50 = 221.50/x
3. Step 3: Cross multiply
   128.50x = 221.50 × 221.50
4. Step 4: Simplify right side
   128.50x = 49,062.25
5. Step 5: Solve for x
   x = 49,062.25/128.50
6. Step 6: Final answer
   x = 381.81