Finding the Fourth Proportional to 20,793.60, 31,129.20 and 12,978.72

Step by Step Solution

1. Step 1: Write the proportion equation
   20,793.60 : 31,129.20 = 12,978.72 : x
2. Step 2: Convert to fraction form
   20,793.60/31,129.20 = 12,978.72/x
3. Step 3: Cross multiply
   20,793.60x = 31,129.20 × 12,978.72
4. Step 4: Simplify right side
   20,793.60x = 404,017,170.62
5. Step 5: Solve for x
   x = 404,017,170.62/20,793.60
6. Step 6: Final answer
   x = 19,429.88