Finding the Fourth Proportional to 1,388.78, 1,917.54 and 916.58

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.78 : 1,917.54 = 916.58 : x
2. Step 2: Convert to fraction form
   1,388.78/1,917.54 = 916.58/x
3. Step 3: Cross multiply
   1,388.78x = 1,917.54 × 916.58
4. Step 4: Simplify right side
   1,388.78x = 1,757,578.81
5. Step 5: Solve for x
   x = 1,757,578.81/1,388.78
6. Step 6: Final answer
   x = 1,265.56