Finding the Fourth Proportional to 1,369.72, 1,890.36 and 780.30

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.72 : 1,890.36 = 780.30 : x
2. Step 2: Convert to fraction form
   1,369.72/1,890.36 = 780.30/x
3. Step 3: Cross multiply
   1,369.72x = 1,890.36 × 780.30
4. Step 4: Simplify right side
   1,369.72x = 1,475,047.91
5. Step 5: Solve for x
   x = 1,475,047.91/1,369.72
6. Step 6: Final answer
   x = 1,076.90