Finding the Fourth Proportional to 1,086.78, 1,499.79 and 644.65

Step by Step Solution

1. Step 1: Write the proportion equation
   1,086.78 : 1,499.79 = 644.65 : x
2. Step 2: Convert to fraction form
   1,086.78/1,499.79 = 644.65/x
3. Step 3: Cross multiply
   1,086.78x = 1,499.79 × 644.65
4. Step 4: Simplify right side
   1,086.78x = 966,839.62
5. Step 5: Solve for x
   x = 966,839.62/1,086.78
6. Step 6: Final answer
   x = 889.64