Finding the Fourth Proportional to 1,189.63, 1,641.69 and 665.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,189.63 : 1,641.69 = 665.78 : x
2. Step 2: Convert to fraction form
   1,189.63/1,641.69 = 665.78/x
3. Step 3: Cross multiply
   1,189.63x = 1,641.69 × 665.78
4. Step 4: Simplify right side
   1,189.63x = 1,093,001.04
5. Step 5: Solve for x
   x = 1,093,001.04/1,189.63
6. Step 6: Final answer
   x = 918.78