Finding the Fourth Proportional to 2,147.78, 3,221.37 and 686.61

Step by Step Solution

1. Step 1: Write the proportion equation
   2,147.78 : 3,221.37 = 686.61 : x
2. Step 2: Convert to fraction form
   2,147.78/3,221.37 = 686.61/x
3. Step 3: Cross multiply
   2,147.78x = 3,221.37 × 686.61
4. Step 4: Simplify right side
   2,147.78x = 2,211,824.86
5. Step 5: Solve for x
   x = 2,211,824.86/2,147.78
6. Step 6: Final answer
   x = 1,029.82