Finding the Fourth Proportional to 1,369.98, 1,890.72 and 780.60

Step by Step Solution

1. Step 1: Write the proportion equation
   1,369.98 : 1,890.72 = 780.60 : x
2. Step 2: Convert to fraction form
   1,369.98/1,890.72 = 780.60/x
3. Step 3: Cross multiply
   1,369.98x = 1,890.72 × 780.60
4. Step 4: Simplify right side
   1,369.98x = 1,475,896.03
5. Step 5: Solve for x
   x = 1,475,896.03/1,369.98
6. Step 6: Final answer
   x = 1,077.31