Finding the Fourth Proportional to 1,388.66, 1,915.81 and 891.23

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.66 : 1,915.81 = 891.23 : x
2. Step 2: Convert to fraction form
   1,388.66/1,915.81 = 891.23/x
3. Step 3: Cross multiply
   1,388.66x = 1,915.81 × 891.23
4. Step 4: Simplify right side
   1,388.66x = 1,707,415.54
5. Step 5: Solve for x
   x = 1,707,415.54/1,388.66
6. Step 6: Final answer
   x = 1,229.54