Finding the Fourth Proportional to 1,139.57, 1,572.63 and 642.23

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.57 : 1,572.63 = 642.23 : x
2. Step 2: Convert to fraction form
   1,139.57/1,572.63 = 642.23/x
3. Step 3: Cross multiply
   1,139.57x = 1,572.63 × 642.23
4. Step 4: Simplify right side
   1,139.57x = 1,009,990.16
5. Step 5: Solve for x
   x = 1,009,990.16/1,139.57
6. Step 6: Final answer
   x = 886.29