Finding the Fourth Proportional to 1,290.78, 1,781.16 and 766.71

Step by Step Solution

1. Step 1: Write the proportion equation
   1,290.78 : 1,781.16 = 766.71 : x
2. Step 2: Convert to fraction form
   1,290.78/1,781.16 = 766.71/x
3. Step 3: Cross multiply
   1,290.78x = 1,781.16 × 766.71
4. Step 4: Simplify right side
   1,290.78x = 1,365,633.18
5. Step 5: Solve for x
   x = 1,365,633.18/1,290.78
6. Step 6: Final answer
   x = 1,057.99