Finding the Fourth Proportional to 1,138.98, 1,571.82 and 641.61

Step by Step Solution

1. Step 1: Write the proportion equation
   1,138.98 : 1,571.82 = 641.61 : x
2. Step 2: Convert to fraction form
   1,138.98/1,571.82 = 641.61/x
3. Step 3: Cross multiply
   1,138.98x = 1,571.82 × 641.61
4. Step 4: Simplify right side
   1,138.98x = 1,008,495.43
5. Step 5: Solve for x
   x = 1,008,495.43/1,138.98
6. Step 6: Final answer
   x = 885.44