Finding the Fourth Proportional to 498.78, 688.26 and 291.78

Step by Step Solution

1. Step 1: Write the proportion equation
   498.78 : 688.26 = 291.78 : x
2. Step 2: Convert to fraction form
   498.78/688.26 = 291.78/x
3. Step 3: Cross multiply
   498.78x = 688.26 × 291.78
4. Step 4: Simplify right side
   498.78x = 200,820.50
5. Step 5: Solve for x
   x = 200,820.50/498.78
6. Step 6: Final answer
   x = 402.62