Finding the Fourth Proportional to 1,218.78, 1,681.88 and 687.69

Step by Step Solution

1. Step 1: Write the proportion equation
   1,218.78 : 1,681.88 = 687.69 : x
2. Step 2: Convert to fraction form
   1,218.78/1,681.88 = 687.69/x
3. Step 3: Cross multiply
   1,218.78x = 1,681.88 × 687.69
4. Step 4: Simplify right side
   1,218.78x = 1,156,608.62
5. Step 5: Solve for x
   x = 1,156,608.62/1,218.78
6. Step 6: Final answer
   x = 948.99