Finding the Fourth Proportional to 1,189.72, 1,641.87 and 665.71

Step by Step Solution

1. Step 1: Write the proportion equation
   1,189.72 : 1,641.87 = 665.71 : x
2. Step 2: Convert to fraction form
   1,189.72/1,641.87 = 665.71/x
3. Step 3: Cross multiply
   1,189.72x = 1,641.87 × 665.71
4. Step 4: Simplify right side
   1,189.72x = 1,093,009.28
5. Step 5: Solve for x
   x = 1,093,009.28/1,189.72
6. Step 6: Final answer
   x = 918.71