Finding the Third Proportional to 391.50 and 622.69

Step by Step Solution

1. Step 1: Write the proportion equation
   391.50 : 622.69 = 622.69 : x
2. Step 2: Convert to fraction form
   391.50/622.69 = 622.69/x
3. Step 3: Cross multiply
   391.50x = 622.69 × 622.69
4. Step 4: Simplify right side
   391.50x = 387,739.72
5. Step 5: Solve for x
   x = 387,739.72/391.50
6. Step 6: Final answer
   x = 990.40