Finding the Fourth Proportional to 20,128.86, 30,178.71 and 10,139.76

Step by Step Solution

1. Step 1: Write the proportion equation
   20,128.86 : 30,178.71 = 10,139.76 : x
2. Step 2: Convert to fraction form
   20,128.86/30,178.71 = 10,139.76/x
3. Step 3: Cross multiply
   20,128.86x = 30,178.71 × 10,139.76
4. Step 4: Simplify right side
   20,128.86x = 306,004,876.51
5. Step 5: Solve for x
   x = 306,004,876.51/20,128.86
6. Step 6: Final answer
   x = 15,202.30