Finding the Fourth Proportional to 21,389.89, 29,495.80 and 12,890.31

Step by Step Solution

1. Step 1: Write the proportion equation
   21,389.89 : 29,495.80 = 12,890.31 : x
2. Step 2: Convert to fraction form
   21,389.89/29,495.80 = 12,890.31/x
3. Step 3: Cross multiply
   21,389.89x = 29,495.80 × 12,890.31
4. Step 4: Simplify right side
   21,389.89x = 380,210,087.56
5. Step 5: Solve for x
   x = 380,210,087.56/21,389.89
6. Step 6: Final answer
   x = 17,775.23