Finding the Fourth Proportional to 2,621.31, 3,929.21 and 1,320.05

Step by Step Solution

1. Step 1: Write the proportion equation
   2,621.31 : 3,929.21 = 1,320.05 : x
2. Step 2: Convert to fraction form
   2,621.31/3,929.21 = 1,320.05/x
3. Step 3: Cross multiply
   2,621.31x = 3,929.21 × 1,320.05
4. Step 4: Simplify right side
   2,621.31x = 5,186,739.73
5. Step 5: Solve for x
   x = 5,186,739.73/2,621.31
6. Step 6: Final answer
   x = 1,978.68