Finding the Fourth Proportional to 1,039.78, 1,558.59 and 423.91

Step by Step Solution

1. Step 1: Write the proportion equation
   1,039.78 : 1,558.59 = 423.91 : x
2. Step 2: Convert to fraction form
   1,039.78/1,558.59 = 423.91/x
3. Step 3: Cross multiply
   1,039.78x = 1,558.59 × 423.91
4. Step 4: Simplify right side
   1,039.78x = 660,701.89
5. Step 5: Solve for x
   x = 660,701.89/1,039.78
6. Step 6: Final answer
   x = 635.42