Finding the Fourth Proportional to 1,388.78, 1,916.33 and 791.05

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.78 : 1,916.33 = 791.05 : x
2. Step 2: Convert to fraction form
   1,388.78/1,916.33 = 791.05/x
3. Step 3: Cross multiply
   1,388.78x = 1,916.33 × 791.05
4. Step 4: Simplify right side
   1,388.78x = 1,515,910.03
5. Step 5: Solve for x
   x = 1,515,910.03/1,388.78
6. Step 6: Final answer
   x = 1,091.54