Finding the Third Proportional to 76.31 and 128.91

Step by Step Solution

1. Step 1: Write the proportion equation
   76.31 : 128.91 = 128.91 : x
2. Step 2: Convert to fraction form
   76.31/128.91 = 128.91/x
3. Step 3: Cross multiply
   76.31x = 128.91 × 128.91
4. Step 4: Simplify right side
   76.31x = 16,616.82
5. Step 5: Solve for x
   x = 16,616.82/76.31
6. Step 6: Final answer
   x = 217.75