Finding the Fourth Proportional to 1,388.75, 1,915.57 and 890.60

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.75 : 1,915.57 = 890.60 : x
2. Step 2: Convert to fraction form
   1,388.75/1,915.57 = 890.60/x
3. Step 3: Cross multiply
   1,388.75x = 1,915.57 × 890.60
4. Step 4: Simplify right side
   1,388.75x = 1,705,992.61
5. Step 5: Solve for x
   x = 1,705,992.61/1,388.75
6. Step 6: Final answer
   x = 1,228.44