Finding the Third Proportional to 12,978 and 21,087

Step by Step Solution

1. Step 1: Write the proportion equation
   12,978 : 21,087 = 21,087 : x
2. Step 2: Convert to fraction form
   12,978/21,087 = 21,087/x
3. Step 3: Cross multiply
   12,978x = 21,087 × 21,087
4. Step 4: Simplify right side
   12,978x = 444,661,569
5. Step 5: Solve for x
   x = 444,661,569/12,978
6. Step 6: Final answer
   x = 34,262.72