Finding the Fourth Proportional to 1,013.78, 1,399.50 and 641.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,013.78 : 1,399.50 = 641.31 : x
2. Step 2: Convert to fraction form
   1,013.78/1,399.50 = 641.31/x
3. Step 3: Cross multiply
   1,013.78x = 1,399.50 × 641.31
4. Step 4: Simplify right side
   1,013.78x = 897,513.35
5. Step 5: Solve for x
   x = 897,513.35/1,013.78
6. Step 6: Final answer
   x = 885.31