Finding the Third Proportional to 12,840 and 20,640

Step by Step Solution

1. Step 1: Write the proportion equation
   12,840 : 20,640 = 20,640 : x
2. Step 2: Convert to fraction form
   12,840/20,640 = 20,640/x
3. Step 3: Cross multiply
   12,840x = 20,640 × 20,640
4. Step 4: Simplify right side
   12,840x = 426,009,600
5. Step 5: Solve for x
   x = 426,009,600/12,840
6. Step 6: Final answer
   x = 33,178.32