Finding the Third Proportional to 138.80 and 213.89

Step by Step Solution

1. Step 1: Write the proportion equation
   138.80 : 213.89 = 213.89 : x
2. Step 2: Convert to fraction form
   138.80/213.89 = 213.89/x
3. Step 3: Cross multiply
   138.80x = 213.89 × 213.89
4. Step 4: Simplify right side
   138.80x = 45,749.20
5. Step 5: Solve for x
   x = 45,749.20/138.80
6. Step 6: Final answer
   x = 329.61