Finding the Fourth Proportional to 1,369.92, 1,890.56 and 780.64

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.92 : 1,890.56 = 780.64 : x
2. Step 2: Convert to fraction form
   1,369.92/1,890.56 = 780.64/x
3. Step 3: Cross multiply
   1,369.92x = 1,890.56 × 780.64
4. Step 4: Simplify right side
   1,369.92x = 1,475,846.76
5. Step 5: Solve for x
   x = 1,475,846.76/1,369.92
6. Step 6: Final answer
   x = 1,077.32