Finding the Fourth Proportional to 1,391.42, 1,920.78 and 919.60

Step by Step Solution

1. Step 1: Write the proportion equation
   1,391.42 : 1,920.78 = 919.60 : x
2. Step 2: Convert to fraction form
   1,391.42/1,920.78 = 919.60/x
3. Step 3: Cross multiply
   1,391.42x = 1,920.78 × 919.60
4. Step 4: Simplify right side
   1,391.42x = 1,766,349.29
5. Step 5: Solve for x
   x = 1,766,349.29/1,391.42
6. Step 6: Final answer
   x = 1,269.46