Finding the Third Proportional to 12,780 and 21,120

Step by Step Solution

1. Step 1: Write the proportion equation
   12,780 : 21,120 = 21,120 : x
2. Step 2: Convert to fraction form
   12,780/21,120 = 21,120/x
3. Step 3: Cross multiply
   12,780x = 21,120 × 21,120
4. Step 4: Simplify right side
   12,780x = 446,054,400
5. Step 5: Solve for x
   x = 446,054,400/12,780
6. Step 6: Final answer
   x = 34,902.54