Finding the Fourth Proportional to 1,128.55, 1,557.72 and 686.60

Step by Step Solution

1. Step 1: Write the proportion equation
   1,128.55 : 1,557.72 = 686.60 : x
2. Step 2: Convert to fraction form
   1,128.55/1,557.72 = 686.60/x
3. Step 3: Cross multiply
   1,128.55x = 1,557.72 × 686.60
4. Step 4: Simplify right side
   1,128.55x = 1,069,530.55
5. Step 5: Solve for x
   x = 1,069,530.55/1,128.55
6. Step 6: Final answer
   x = 947.70