Finding the Fourth Proportional to 1,388.40, 2,077.79 and 861.09

Step by Step Solution

1. Step 1: Write the proportion equation
   1,388.40 : 2,077.79 = 861.09 : x
2. Step 2: Convert to fraction form
   1,388.40/2,077.79 = 861.09/x
3. Step 3: Cross multiply
   1,388.40x = 2,077.79 × 861.09
4. Step 4: Simplify right side
   1,388.40x = 1,789,159.89
5. Step 5: Solve for x
   x = 1,789,159.89/1,388.40
6. Step 6: Final answer
   x = 1,288.65