Finding the Fourth Proportional to 1,139.46, 1,572.17 and 641.91

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.46 : 1,572.17 = 641.91 : x
2. Step 2: Convert to fraction form
   1,139.46/1,572.17 = 641.91/x
3. Step 3: Cross multiply
   1,139.46x = 1,572.17 × 641.91
4. Step 4: Simplify right side
   1,139.46x = 1,009,191.64
5. Step 5: Solve for x
   x = 1,009,191.64/1,139.46
6. Step 6: Final answer
   x = 885.68