Finding the Third Proportional to 429.89 and 643.78

Step by Step Solution

1. Step 1: Write the proportion equation
   429.89 : 643.78 = 643.78 : x
2. Step 2: Convert to fraction form
   429.89/643.78 = 643.78/x
3. Step 3: Cross multiply
   429.89x = 643.78 × 643.78
4. Step 4: Simplify right side
   429.89x = 414,454.30
5. Step 5: Solve for x
   x = 414,454.30/429.89
6. Step 6: Final answer
   x = 964.09