Finding the Fourth Proportional to 1,189.71, 1,641.81 and 665.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,189.71 : 1,641.81 = 665.78 : x
2. Step 2: Convert to fraction form
   1,189.71/1,641.81 = 665.78/x
3. Step 3: Cross multiply
   1,189.71x = 1,641.81 × 665.78
4. Step 4: Simplify right side
   1,189.71x = 1,093,076.05
5. Step 5: Solve for x
   x = 1,093,076.05/1,189.71
6. Step 6: Final answer
   x = 918.78