Finding the Fourth Proportional to 1,216.45, 1,678.54 and 685.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,216.45 : 1,678.54 = 685.31 : x
2. Step 2: Convert to fraction form
   1,216.45/1,678.54 = 685.31/x
3. Step 3: Cross multiply
   1,216.45x = 1,678.54 × 685.31
4. Step 4: Simplify right side
   1,216.45x = 1,150,320.87
5. Step 5: Solve for x
   x = 1,150,320.87/1,216.45
6. Step 6: Final answer
   x = 945.64