Finding the Fourth Proportional to 1,222.35, 1,686.39 and 780.15

Step by Step Solution

1. Step 1: Write the proportion equation
   1,222.35 : 1,686.39 = 780.15 : x
2. Step 2: Convert to fraction form
   1,222.35/1,686.39 = 780.15/x
3. Step 3: Cross multiply
   1,222.35x = 1,686.39 × 780.15
4. Step 4: Simplify right side
   1,222.35x = 1,315,637.16
5. Step 5: Solve for x
   x = 1,315,637.16/1,222.35
6. Step 6: Final answer
   x = 1,076.32