Finding the Fourth Proportional to 1,388.78, 1,916.43 and 767.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.78 : 1,916.43 = 767.78 : x
2. Step 2: Convert to fraction form
   1,388.78/1,916.43 = 767.78/x
3. Step 3: Cross multiply
   1,388.78x = 1,916.43 × 767.78
4. Step 4: Simplify right side
   1,388.78x = 1,471,396.63
5. Step 5: Solve for x
   x = 1,471,396.63/1,388.78
6. Step 6: Final answer
   x = 1,059.49