Finding the Fourth Proportional to 1,287.25, 1,776.54 and 789.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,287.25 : 1,776.54 = 789.78 : x
2. Step 2: Convert to fraction form
   1,287.25/1,776.54 = 789.78/x
3. Step 3: Cross multiply
   1,287.25x = 1,776.54 × 789.78
4. Step 4: Simplify right side
   1,287.25x = 1,403,075.76
5. Step 5: Solve for x
   x = 1,403,075.76/1,287.25
6. Step 6: Final answer
   x = 1,089.98