Finding the Fourth Proportional to 31,170, 42,997.28 and 20,399.92

Step by Step Solution

1. Step 1: Write the proportion equation
   31,170 : 42,997.28 = 20,399.92 : x
2. Step 2: Convert to fraction form
   31,170/42,997.28 = 20,399.92/x
3. Step 3: Cross multiply
   31,170x = 42,997.28 × 20,399.92
4. Step 4: Simplify right side
   31,170x = 877,141,072.22
5. Step 5: Solve for x
   x = 877,141,072.22/31,170
6. Step 6: Final answer
   x = 28,140.55