Finding the Fourth Proportional to 1,222.74, 1,685.61 and 780.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,222.74 : 1,685.61 = 780.30 : x
2. Step 2: Convert to fraction form
   1,222.74/1,685.61 = 780.30/x
3. Step 3: Cross multiply
   1,222.74x = 1,685.61 × 780.30
4. Step 4: Simplify right side
   1,222.74x = 1,315,281.48
5. Step 5: Solve for x
   x = 1,315,281.48/1,222.74
6. Step 6: Final answer
   x = 1,075.68