Finding the Third Proportional to 21.09 and 42.61

Step by Step Solution

1. Step 1: Write the proportion equation
   21.09 : 42.61 = 42.61 : x
2. Step 2: Convert to fraction form
   21.09/42.61 = 42.61/x
3. Step 3: Cross multiply
   21.09x = 42.61 × 42.61
4. Step 4: Simplify right side
   21.09x = 1,815.56
5. Step 5: Solve for x
   x = 1,815.56/21.09
6. Step 6: Final answer
   x = 86.07