Finding the Fourth Proportional to 1,379.72, 2,070.49 and 685.80

Step by Step Solution

1. Step 1: Write the proportion equation
   1,379.72 : 2,070.49 = 685.80 : x
2. Step 2: Convert to fraction form
   1,379.72/2,070.49 = 685.80/x
3. Step 3: Cross multiply
   1,379.72x = 2,070.49 × 685.80
4. Step 4: Simplify right side
   1,379.72x = 1,419,942.04
5. Step 5: Solve for x
   x = 1,419,942.04/1,379.72
6. Step 6: Final answer
   x = 1,029.15