Finding the Fourth Proportional to 1,086.78, 1,499.67 and 644.79

Step by Step Solution

1. Step 1: Write the proportion equation
   1,086.78 : 1,499.67 = 644.79 : x
2. Step 2: Convert to fraction form
   1,086.78/1,499.67 = 644.79/x
3. Step 3: Cross multiply
   1,086.78x = 1,499.67 × 644.79
4. Step 4: Simplify right side
   1,086.78x = 966,972.22
5. Step 5: Solve for x
   x = 966,972.22/1,086.78
6. Step 6: Final answer
   x = 889.76