Finding the Third Proportional to 410.77 and 640.72

Step by Step Solution

1. Step 1: Write the proportion equation
   410.77 : 640.72 = 640.72 : x
2. Step 2: Convert to fraction form
   410.77/640.72 = 640.72/x
3. Step 3: Cross multiply
   410.77x = 640.72 × 640.72
4. Step 4: Simplify right side
   410.77x = 410,525.52
5. Step 5: Solve for x
   x = 410,525.52/410.77
6. Step 6: Final answer
   x = 999.39