Finding the Third Proportional to 12,420 and 17,780

Step by Step Solution

1. Step 1: Write the proportion equation
   12,420 : 17,780 = 17,780 : x
2. Step 2: Convert to fraction form
   12,420/17,780 = 17,780/x
3. Step 3: Cross multiply
   12,420x = 17,780 × 17,780
4. Step 4: Simplify right side
   12,420x = 316,128,400
5. Step 5: Solve for x
   x = 316,128,400/12,420
6. Step 6: Final answer
   x = 25,453.17