Finding the Fourth Proportional to 1,139.86, 1,572.91 and 642.44

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.86 : 1,572.91 = 642.44 : x
2. Step 2: Convert to fraction form
   1,139.86/1,572.91 = 642.44/x
3. Step 3: Cross multiply
   1,139.86x = 1,572.91 × 642.44
4. Step 4: Simplify right side
   1,139.86x = 1,010,500.30
5. Step 5: Solve for x
   x = 1,010,500.30/1,139.86
6. Step 6: Final answer
   x = 886.51