Finding the Fourth Proportional to 1,320.72, 1,978.24 and 857.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,320.72 : 1,978.24 = 857.15 : x
2. Step 2: Convert to fraction form
   1,320.72/1,978.24 = 857.15/x
3. Step 3: Cross multiply
   1,320.72x = 1,978.24 × 857.15
4. Step 4: Simplify right side
   1,320.72x = 1,695,640.67
5. Step 5: Solve for x
   x = 1,695,640.67/1,320.72
6. Step 6: Final answer
   x = 1,283.88