Finding the Fourth Proportional to 1,387.86, 1,915.41 and 890.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,387.86 : 1,915.41 = 890.31 : x
2. Step 2: Convert to fraction form
   1,387.86/1,915.41 = 890.31/x
3. Step 3: Cross multiply
   1,387.86x = 1,915.41 × 890.31
4. Step 4: Simplify right side
   1,387.86x = 1,705,308.68
5. Step 5: Solve for x
   x = 1,705,308.68/1,387.86
6. Step 6: Final answer
   x = 1,228.73