Finding the Fourth Proportional to 1,389.80, 2,081.90 and 868.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,389.80 : 2,081.90 = 868.20 : x
2. Step 2: Convert to fraction form
   1,389.80/2,081.90 = 868.20/x
3. Step 3: Cross multiply
   1,389.80x = 2,081.90 × 868.20
4. Step 4: Simplify right side
   1,389.80x = 1,807,505.58
5. Step 5: Solve for x
   x = 1,807,505.58/1,389.80
6. Step 6: Final answer
   x = 1,300.55