Finding the Fourth Proportional to 1,081.12, 1,491.72 and 638.96

Step by Step Solution

1. Step 1: Write the proportion equation
   1,081.12 : 1,491.72 = 638.96 : x
2. Step 2: Convert to fraction form
   1,081.12/1,491.72 = 638.96/x
3. Step 3: Cross multiply
   1,081.12x = 1,491.72 × 638.96
4. Step 4: Simplify right side
   1,081.12x = 953,149.41
5. Step 5: Solve for x
   x = 953,149.41/1,081.12
6. Step 6: Final answer
   x = 881.63