Finding the Fourth Proportional to 498.88, 688.61 and 405.55

Step by Step Solution

1. Step 1: Write the proportion equation
   498.88 : 688.61 = 405.55 : x
2. Step 2: Convert to fraction form
   498.88/688.61 = 405.55/x
3. Step 3: Cross multiply
   498.88x = 688.61 × 405.55
4. Step 4: Simplify right side
   498.88x = 279,265.79
5. Step 5: Solve for x
   x = 279,265.79/498.88
6. Step 6: Final answer
   x = 559.79