Finding the Fourth Proportional to 1,139.72, 1,572.83 and 642.33

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.72 : 1,572.83 = 642.33 : x
2. Step 2: Convert to fraction form
   1,139.72/1,572.83 = 642.33/x
3. Step 3: Cross multiply
   1,139.72x = 1,572.83 × 642.33
4. Step 4: Simplify right side
   1,139.72x = 1,010,272.68
5. Step 5: Solve for x
   x = 1,010,272.68/1,139.72
6. Step 6: Final answer
   x = 886.43