Finding the Fourth Proportional to 2,139.53, 3,209.75 and 678.78

Step by Step Solution

1. Step 1: Write the proportion equation
   2,139.53 : 3,209.75 = 678.78 : x
2. Step 2: Convert to fraction form
   2,139.53/3,209.75 = 678.78/x
3. Step 3: Cross multiply
   2,139.53x = 3,209.75 × 678.78
4. Step 4: Simplify right side
   2,139.53x = 2,178,710.71
5. Step 5: Solve for x
   x = 2,178,710.71/2,139.53
6. Step 6: Final answer
   x = 1,018.32