Finding the Fourth Proportional to 2,139.48, 3,209.88 and 678.72

Step by Step Solution

1. Step 1: Write the proportion equation
   2,139.48 : 3,209.88 = 678.72 : x
2. Step 2: Convert to fraction form
   2,139.48/3,209.88 = 678.72/x
3. Step 3: Cross multiply
   2,139.48x = 3,209.88 × 678.72
4. Step 4: Simplify right side
   2,139.48x = 2,178,609.75
5. Step 5: Solve for x
   x = 2,178,609.75/2,139.48
6. Step 6: Final answer
   x = 1,018.29