Finding the Fourth Proportional to 1,390.38, 2,086.05 and 870.77

Step by Step Solution

1. Step 1: Write the proportion equation
   1,390.38 : 2,086.05 = 870.77 : x
2. Step 2: Convert to fraction form
   1,390.38/2,086.05 = 870.77/x
3. Step 3: Cross multiply
   1,390.38x = 2,086.05 × 870.77
4. Step 4: Simplify right side
   1,390.38x = 1,816,459.33
5. Step 5: Solve for x
   x = 1,816,459.33/1,390.38
6. Step 6: Final answer
   x = 1,306.45