Finding the Fourth Proportional to 1,380.81, 1,905.01 and 821.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.81 : 1,905.01 = 821.30 : x
2. Step 2: Convert to fraction form
   1,380.81/1,905.01 = 821.30/x
3. Step 3: Cross multiply
   1,380.81x = 1,905.01 × 821.30
4. Step 4: Simplify right side
   1,380.81x = 1,564,587.42
5. Step 5: Solve for x
   x = 1,564,587.42/1,380.81
6. Step 6: Final answer
   x = 1,133.09