Finding the Fourth Proportional to 1,380.88, 1,905.60 and 856.96

Step by Step Solution

1. Step 1: Write the proportion equation
   1,380.88 : 1,905.60 = 856.96 : x
2. Step 2: Convert to fraction form
   1,380.88/1,905.60 = 856.96/x
3. Step 3: Cross multiply
   1,380.88x = 1,905.60 × 856.96
4. Step 4: Simplify right side
   1,380.88x = 1,633,022.98
5. Step 5: Solve for x
   x = 1,633,022.98/1,380.88
6. Step 6: Final answer
   x = 1,182.60