Finding the Fourth Proportional to 1,086.59, 1,628.18 and 840.40

Step by Step Solution

1. Step 1: Write the proportion equation
   1,086.59 : 1,628.18 = 840.40 : x
2. Step 2: Convert to fraction form
   1,086.59/1,628.18 = 840.40/x
3. Step 3: Cross multiply
   1,086.59x = 1,628.18 × 840.40
4. Step 4: Simplify right side
   1,086.59x = 1,368,322.47
5. Step 5: Solve for x
   x = 1,368,322.47/1,086.59
6. Step 6: Final answer
   x = 1,259.28