Finding the Fourth Proportional to 1,209.78, 1,669.61 and 685.85

Step by Step Solution

1. Step 1: Write the proportion equation
   1,209.78 : 1,669.61 = 685.85 : x
2. Step 2: Convert to fraction form
   1,209.78/1,669.61 = 685.85/x
3. Step 3: Cross multiply
   1,209.78x = 1,669.61 × 685.85
4. Step 4: Simplify right side
   1,209.78x = 1,145,095.39
5. Step 5: Solve for x
   x = 1,145,095.39/1,209.78
6. Step 6: Final answer
   x = 946.53