Finding the Fourth Proportional to 21,328.82, 31,944.78 and 12,990.48

Step by Step Solution

1. Step 1: Write the proportion equation
   21,328.82 : 31,944.78 = 12,990.48 : x
2. Step 2: Convert to fraction form
   21,328.82/31,944.78 = 12,990.48/x
3. Step 3: Cross multiply
   21,328.82x = 31,944.78 × 12,990.48
4. Step 4: Simplify right side
   21,328.82x = 414,977,905.90
5. Step 5: Solve for x
   x = 414,977,905.90/21,328.82
6. Step 6: Final answer
   x = 19,456.21