Finding the Fourth Proportional to 1,128.90, 1,557.38 and 686.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,128.90 : 1,557.38 = 686.78 : x
2. Step 2: Convert to fraction form
   1,128.90/1,557.38 = 686.78/x
3. Step 3: Cross multiply
   1,128.90x = 1,557.38 × 686.78
4. Step 4: Simplify right side
   1,128.90x = 1,069,566.22
5. Step 5: Solve for x
   x = 1,069,566.22/1,128.90
6. Step 6: Final answer
   x = 947.44