Finding the Fourth Proportional to 20,861, 28,788.18 and 12,479.48

Step by Step Solution

1. Step 1: Write the proportion equation
   20,861 : 28,788.18 = 12,479.48 : x
2. Step 2: Convert to fraction form
   20,861/28,788.18 = 12,479.48/x
3. Step 3: Cross multiply
   20,861x = 28,788.18 × 12,479.48
4. Step 4: Simplify right side
   20,861x = 359,261,516.55
5. Step 5: Solve for x
   x = 359,261,516.55/20,861
6. Step 6: Final answer
   x = 17,221.68