Finding the Fourth Proportional to 1,080.78, 1,491.54 and 638.58

Step by Step Solution

1. Step 1: Write the proportion equation
   1,080.78 : 1,491.54 = 638.58 : x
2. Step 2: Convert to fraction form
   1,080.78/1,491.54 = 638.58/x
3. Step 3: Cross multiply
   1,080.78x = 1,491.54 × 638.58
4. Step 4: Simplify right side
   1,080.78x = 952,467.61
5. Step 5: Solve for x
   x = 952,467.61/1,080.78
6. Step 6: Final answer
   x = 881.28