Finding the Fourth Proportional to 1,086.40, 1,499.12 and 644.32

Step by Step Solution

1. Step 1: Write the proportion equation
   1,086.40 : 1,499.12 = 644.32 : x
2. Step 2: Convert to fraction form
   1,086.40/1,499.12 = 644.32/x
3. Step 3: Cross multiply
   1,086.40x = 1,499.12 × 644.32
4. Step 4: Simplify right side
   1,086.40x = 965,913.00
5. Step 5: Solve for x
   x = 965,913.00/1,086.40
6. Step 6: Final answer
   x = 889.10