Finding the Fourth Proportional to 1,369.78, 1,890.30 and 780.28

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.78 : 1,890.30 = 780.28 : x
2. Step 2: Convert to fraction form
   1,369.78/1,890.30 = 780.28/x
3. Step 3: Cross multiply
   1,369.78x = 1,890.30 × 780.28
4. Step 4: Simplify right side
   1,369.78x = 1,474,963.28
5. Step 5: Solve for x
   x = 1,474,963.28/1,369.78
6. Step 6: Final answer
   x = 1,076.79