Finding the Fourth Proportional to 1,391.85, 2,086.15 and 813.51

Step by Step Solution

1. Step 1: Write the proportion equation
   1,391.85 : 2,086.15 = 813.51 : x
2. Step 2: Convert to fraction form
   1,391.85/2,086.15 = 813.51/x
3. Step 3: Cross multiply
   1,391.85x = 2,086.15 × 813.51
4. Step 4: Simplify right side
   1,391.85x = 1,697,103.89
5. Step 5: Solve for x
   x = 1,697,103.89/1,391.85
6. Step 6: Final answer
   x = 1,219.32