Finding the Fourth Proportional to 1,139.25, 1,571.88 and 641.89

Step by Step Solution

1. Step 1: Write the proportion equation
   1,139.25 : 1,571.88 = 641.89 : x
2. Step 2: Convert to fraction form
   1,139.25/1,571.88 = 641.89/x
3. Step 3: Cross multiply
   1,139.25x = 1,571.88 × 641.89
4. Step 4: Simplify right side
   1,139.25x = 1,008,967.80
5. Step 5: Solve for x
   x = 1,008,967.80/1,139.25
6. Step 6: Final answer
   x = 885.65