Finding the Third Proportional to 8,640 and 12,690

Step by Step Solution

1. Step 1: Write the proportion equation
   8,640 : 12,690 = 12,690 : x
2. Step 2: Convert to fraction form
   8,640/12,690 = 12,690/x
3. Step 3: Cross multiply
   8,640x = 12,690 × 12,690
4. Step 4: Simplify right side
   8,640x = 161,036,100
5. Step 5: Solve for x
   x = 161,036,100/8,640
6. Step 6: Final answer
   x = 18,638.44