Finding the Fourth Proportional to 498.57, 687.99 and 288.72

Step by Step Solution

1. Step 1: Write the proportion equation
   498.57 : 687.99 = 288.72 : x
2. Step 2: Convert to fraction form
   498.57/687.99 = 288.72/x
3. Step 3: Cross multiply
   498.57x = 687.99 × 288.72
4. Step 4: Simplify right side
   498.57x = 198,636.47
5. Step 5: Solve for x
   x = 198,636.47/498.57
6. Step 6: Final answer
   x = 398.41