Finding the Fourth Proportional to 1,355.90, 1,871.15 and 766.40

Step by Step Solution

1. Step 1: Write the proportion equation
   1,355.90 : 1,871.15 = 766.40 : x
2. Step 2: Convert to fraction form
   1,355.90/1,871.15 = 766.40/x
3. Step 3: Cross multiply
   1,355.90x = 1,871.15 × 766.40
4. Step 4: Simplify right side
   1,355.90x = 1,434,036.17
5. Step 5: Solve for x
   x = 1,434,036.17/1,355.90
6. Step 6: Final answer
   x = 1,057.63