Finding the Third Proportional to 8,142 and 12,990

Step by Step Solution

1. Step 1: Write the proportion equation
   8,142 : 12,990 = 12,990 : x
2. Step 2: Convert to fraction form
   8,142/12,990 = 12,990/x
3. Step 3: Cross multiply
   8,142x = 12,990 × 12,990
4. Step 4: Simplify right side
   8,142x = 168,740,100
5. Step 5: Solve for x
   x = 168,740,100/8,142
6. Step 6: Final answer
   x = 20,724.65