Finding the Fourth Proportional to 1,280.72, 1,921.69 and 664.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,280.72 : 1,921.69 = 664.31 : x
2. Step 2: Convert to fraction form
   1,280.72/1,921.69 = 664.31/x
3. Step 3: Cross multiply
   1,280.72x = 1,921.69 × 664.31
4. Step 4: Simplify right side
   1,280.72x = 1,276,597.88
5. Step 5: Solve for x
   x = 1,276,597.88/1,280.72
6. Step 6: Final answer
   x = 996.78