Finding the Fourth Proportional to 1,223.71, 1,688.72 and 664.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,223.71 : 1,688.72 = 664.20 : x
2. Step 2: Convert to fraction form
   1,223.71/1,688.72 = 664.20/x
3. Step 3: Cross multiply
   1,223.71x = 1,688.72 × 664.20
4. Step 4: Simplify right side
   1,223.71x = 1,121,644.50
5. Step 5: Solve for x
   x = 1,121,644.50/1,223.71
6. Step 6: Final answer
   x = 916.60