Finding the Fourth Proportional to 1,188.72, 1,640.39 and 664.79

Step by Step Solution

1. Step 1: Write the proportion equation
   1,188.72 : 1,640.39 = 664.79 : x
2. Step 2: Convert to fraction form
   1,188.72/1,640.39 = 664.79/x
3. Step 3: Cross multiply
   1,188.72x = 1,640.39 × 664.79
4. Step 4: Simplify right side
   1,188.72x = 1,090,503.34
5. Step 5: Solve for x
   x = 1,090,503.34/1,188.72
6. Step 6: Final answer
   x = 917.38