Finding the Fourth Proportional to 2,139.74, 3,209.69 and 678.86

Step by Step Solution

1. Step 1: Write the proportion equation
   2,139.74 : 3,209.69 = 678.86 : x
2. Step 2: Convert to fraction form
   2,139.74/3,209.69 = 678.86/x
3. Step 3: Cross multiply
   2,139.74x = 3,209.69 × 678.86
4. Step 4: Simplify right side
   2,139.74x = 2,178,930.15
5. Step 5: Solve for x
   x = 2,178,930.15/2,139.74
6. Step 6: Final answer
   x = 1,018.32