Finding the Fourth Proportional to 1,288.16, 1,776.72 and 816.20

Step by Step Solution

1. Step 1: Write the proportion equation
   1,288.16 : 1,776.72 = 816.20 : x
2. Step 2: Convert to fraction form
   1,288.16/1,776.72 = 816.20/x
3. Step 3: Cross multiply
   1,288.16x = 1,776.72 × 816.20
4. Step 4: Simplify right side
   1,288.16x = 1,450,158.86
5. Step 5: Solve for x
   x = 1,450,158.86/1,288.16
6. Step 6: Final answer
   x = 1,125.76