Finding the Fourth Proportional to 1,380.21, 1,904.34 and 820.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.21 : 1,904.34 = 820.80 : x
2. Step 2: Convert to fraction form
   1,380.21/1,904.34 = 820.80/x
3. Step 3: Cross multiply
   1,380.21x = 1,904.34 × 820.80
4. Step 4: Simplify right side
   1,380.21x = 1,563,082.27
5. Step 5: Solve for x
   x = 1,563,082.27/1,380.21
6. Step 6: Final answer
   x = 1,132.50