Finding the Fourth Proportional to 2,665.21, 3,998.25 and 815.89

Step by Step Solution

1. Step 1: Write the proportion equation
   2,665.21 : 3,998.25 = 815.89 : x
2. Step 2: Convert to fraction form
   2,665.21/3,998.25 = 815.89/x
3. Step 3: Cross multiply
   2,665.21x = 3,998.25 × 815.89
4. Step 4: Simplify right side
   2,665.21x = 3,262,132.19
5. Step 5: Solve for x
   x = 3,262,132.19/2,665.21
6. Step 6: Final answer
   x = 1,223.97