Finding the Fourth Proportional to 1,139.38, 1,572.50 and 642.18

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.38 : 1,572.50 = 642.18 : x
2. Step 2: Convert to fraction form
   1,139.38/1,572.50 = 642.18/x
3. Step 3: Cross multiply
   1,139.38x = 1,572.50 × 642.18
4. Step 4: Simplify right side
   1,139.38x = 1,009,823.09
5. Step 5: Solve for x
   x = 1,009,823.09/1,139.38
6. Step 6: Final answer
   x = 886.29