Finding the Fourth Proportional to 1,211.72, 1,672.24 and 687.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,211.72 : 1,672.24 = 687.78 : x
2. Step 2: Convert to fraction form
   1,211.72/1,672.24 = 687.78/x
3. Step 3: Cross multiply
   1,211.72x = 1,672.24 × 687.78
4. Step 4: Simplify right side
   1,211.72x = 1,150,133.23
5. Step 5: Solve for x
   x = 1,150,133.23/1,211.72
6. Step 6: Final answer
   x = 949.17