Finding the Fourth Proportional to 1,139.69, 1,572.86 and 642.35

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.69 : 1,572.86 = 642.35 : x
2. Step 2: Convert to fraction form
   1,139.69/1,572.86 = 642.35/x
3. Step 3: Cross multiply
   1,139.69x = 1,572.86 × 642.35
4. Step 4: Simplify right side
   1,139.69x = 1,010,315.54
5. Step 5: Solve for x
   x = 1,010,315.54/1,139.69
6. Step 6: Final answer
   x = 886.49