Finding the Third Proportional to 401.20 and 636.61

Step by Step Solution

1. Step 1: Write the proportion equation
   401.20 : 636.61 = 636.61 : x
2. Step 2: Convert to fraction form
   401.20/636.61 = 636.61/x
3. Step 3: Cross multiply
   401.20x = 636.61 × 636.61
4. Step 4: Simplify right side
   401.20x = 405,271.50
5. Step 5: Solve for x
   x = 405,271.50/401.20
6. Step 6: Final answer
   x = 1,010.14