Finding the Fourth Proportional to 1,388.79, 1,915.77 and 890.87

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.79 : 1,915.77 = 890.87 : x
2. Step 2: Convert to fraction form
   1,388.79/1,915.77 = 890.87/x
3. Step 3: Cross multiply
   1,388.79x = 1,915.77 × 890.87
4. Step 4: Simplify right side
   1,388.79x = 1,706,697.57
5. Step 5: Solve for x
   x = 1,706,697.57/1,388.79
6. Step 6: Final answer
   x = 1,228.91