Finding the Fourth Proportional to 1,380.78, 1,905.48 and 856.50

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.78 : 1,905.48 = 856.50 : x
2. Step 2: Convert to fraction form
   1,380.78/1,905.48 = 856.50/x
3. Step 3: Cross multiply
   1,380.78x = 1,905.48 × 856.50
4. Step 4: Simplify right side
   1,380.78x = 1,632,043.62
5. Step 5: Solve for x
   x = 1,632,043.62/1,380.78
6. Step 6: Final answer
   x = 1,181.97