Finding the Fourth Proportional to 1,369.50, 1,889.89 and 780

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.50 : 1,889.89 = 780 : x
2. Step 2: Convert to fraction form
   1,369.50/1,889.89 = 780/x
3. Step 3: Cross multiply
   1,369.50x = 1,889.89 × 780
4. Step 4: Simplify right side
   1,369.50x = 1,474,114.20
5. Step 5: Solve for x
   x = 1,474,114.20/1,369.50
6. Step 6: Final answer
   x = 1,076.39