Finding the Fourth Proportional to 1,222.68, 1,687.20 and 780.72

Step by Step Solution

1. Step 1: Write the proportion equation
   1,222.68 : 1,687.20 = 780.72 : x
2. Step 2: Convert to fraction form
   1,222.68/1,687.20 = 780.72/x
3. Step 3: Cross multiply
   1,222.68x = 1,687.20 × 780.72
4. Step 4: Simplify right side
   1,222.68x = 1,317,230.78
5. Step 5: Solve for x
   x = 1,317,230.78/1,222.68
6. Step 6: Final answer
   x = 1,077.33