Finding the Fourth Proportional to 1,388.46, 1,916.04 and 915.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.46 : 1,916.04 = 915.78 : x
2. Step 2: Convert to fraction form
   1,388.46/1,916.04 = 915.78/x
3. Step 3: Cross multiply
   1,388.46x = 1,916.04 × 915.78
4. Step 4: Simplify right side
   1,388.46x = 1,754,671.11
5. Step 5: Solve for x
   x = 1,754,671.11/1,388.46
6. Step 6: Final answer
   x = 1,263.75