Finding the Fourth Proportional to 1,139.83, 1,572.95 and 642.56

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.83 : 1,572.95 = 642.56 : x
2. Step 2: Convert to fraction form
   1,139.83/1,572.95 = 642.56/x
3. Step 3: Cross multiply
   1,139.83x = 1,572.95 × 642.56
4. Step 4: Simplify right side
   1,139.83x = 1,010,708.49
5. Step 5: Solve for x
   x = 1,010,708.49/1,139.83
6. Step 6: Final answer
   x = 886.72