Finding the Fourth Proportional to 1,388.40, 1,915.50 and 891.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.40 : 1,915.50 = 891.30 : x
2. Step 2: Convert to fraction form
   1,388.40/1,915.50 = 891.30/x
3. Step 3: Cross multiply
   1,388.40x = 1,915.50 × 891.30
4. Step 4: Simplify right side
   1,388.40x = 1,707,285.15
5. Step 5: Solve for x
   x = 1,707,285.15/1,388.40
6. Step 6: Final answer
   x = 1,229.68