Finding the Fourth Proportional to 1,139.42, 1,572.42 and 642.05

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.42 : 1,572.42 = 642.05 : x
2. Step 2: Convert to fraction form
   1,139.42/1,572.42 = 642.05/x
3. Step 3: Cross multiply
   1,139.42x = 1,572.42 × 642.05
4. Step 4: Simplify right side
   1,139.42x = 1,009,564.40
5. Step 5: Solve for x
   x = 1,009,564.40/1,139.42
6. Step 6: Final answer
   x = 886.04