Finding the Fourth Proportional to 1,139.20, 1,572.04 and 641.88

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.20 : 1,572.04 = 641.88 : x
2. Step 2: Convert to fraction form
   1,139.20/1,572.04 = 641.88/x
3. Step 3: Cross multiply
   1,139.20x = 1,572.04 × 641.88
4. Step 4: Simplify right side
   1,139.20x = 1,009,061.04
5. Step 5: Solve for x
   x = 1,009,061.04/1,139.20
6. Step 6: Final answer
   x = 885.76