Finding the Fourth Proportional to 2,139.75, 3,209.72 and 678.87

Step by Step Solution

1. Step 1: Write the proportion equation
   2,139.75 : 3,209.72 = 678.87 : x
2. Step 2: Convert to fraction form
   2,139.75/3,209.72 = 678.87/x
3. Step 3: Cross multiply
   2,139.75x = 3,209.72 × 678.87
4. Step 4: Simplify right side
   2,139.75x = 2,178,982.62
5. Step 5: Solve for x
   x = 2,178,982.62/2,139.75
6. Step 6: Final answer
   x = 1,018.34