Finding the Third Proportional to 21.40 and 42.09

Step by Step Solution

1. Step 1: Write the proportion equation
   21.40 : 42.09 = 42.09 : x
2. Step 2: Convert to fraction form
   21.40/42.09 = 42.09/x
3. Step 3: Cross multiply
   21.40x = 42.09 × 42.09
4. Step 4: Simplify right side
   21.40x = 1,771.63
5. Step 5: Solve for x
   x = 1,771.63/21.40
6. Step 6: Final answer
   x = 82.78