Finding the Fourth Proportional to 1,369.72, 1,890.23 and 780.31

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.72 : 1,890.23 = 780.31 : x
2. Step 2: Convert to fraction form
   1,369.72/1,890.23 = 780.31/x
3. Step 3: Cross multiply
   1,369.72x = 1,890.23 × 780.31
4. Step 4: Simplify right side
   1,369.72x = 1,474,965.37
5. Step 5: Solve for x
   x = 1,474,965.37/1,369.72
6. Step 6: Final answer
   x = 1,076.84