Finding the Fourth Proportional to 1,288.78, 1,778.47 and 699.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,288.78 : 1,778.47 = 699.30 : x
2. Step 2: Convert to fraction form
   1,288.78/1,778.47 = 699.30/x
3. Step 3: Cross multiply
   1,288.78x = 1,778.47 × 699.30
4. Step 4: Simplify right side
   1,288.78x = 1,243,682.32
5. Step 5: Solve for x
   x = 1,243,682.32/1,288.78
6. Step 6: Final answer
   x = 965.01