Finding the Fourth Proportional to 1,139.55, 1,572.42 and 642.10

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.55 : 1,572.42 = 642.10 : x
2. Step 2: Convert to fraction form
   1,139.55/1,572.42 = 642.10/x
3. Step 3: Cross multiply
   1,139.55x = 1,572.42 × 642.10
4. Step 4: Simplify right side
   1,139.55x = 1,009,650.88
5. Step 5: Solve for x
   x = 1,009,650.88/1,139.55
6. Step 6: Final answer
   x = 886.01