Finding the Fourth Proportional to 1,216.35, 1,678.55 and 685.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,216.35 : 1,678.55 = 685.20 : x
2. Step 2: Convert to fraction form
   1,216.35/1,678.55 = 685.20/x
3. Step 3: Cross multiply
   1,216.35x = 1,678.55 × 685.20
4. Step 4: Simplify right side
   1,216.35x = 1,150,139.03
5. Step 5: Solve for x
   x = 1,150,139.03/1,216.35
6. Step 6: Final answer
   x = 945.57