Finding the Fourth Proportional to 1,380.20, 1,905.42 and 1,006.78

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.20 : 1,905.42 = 1,006.78 : x
2. Step 2: Convert to fraction form
   1,380.20/1,905.42 = 1,006.78/x
3. Step 3: Cross multiply
   1,380.20x = 1,905.42 × 1,006.78
4. Step 4: Simplify right side
   1,380.20x = 1,918,338.75
5. Step 5: Solve for x
   x = 1,918,338.75/1,380.20
6. Step 6: Final answer
   x = 1,389.90