Finding the Fourth Proportional to 1,380.15, 1,904.49 and 820.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.15 : 1,904.49 = 820.80 : x
2. Step 2: Convert to fraction form
   1,380.15/1,904.49 = 820.80/x
3. Step 3: Cross multiply
   1,380.15x = 1,904.49 × 820.80
4. Step 4: Simplify right side
   1,380.15x = 1,563,205.39
5. Step 5: Solve for x
   x = 1,563,205.39/1,380.15
6. Step 6: Final answer
   x = 1,132.63