Finding the Third Proportional to 11.69 and 15.78

Step by Step Solution

1. Step 1: Write the proportion equation
   11.69 : 15.78 = 15.78 : x
2. Step 2: Convert to fraction form
   11.69/15.78 = 15.78/x
3. Step 3: Cross multiply
   11.69x = 15.78 × 15.78
4. Step 4: Simplify right side
   11.69x = 249.05
5. Step 5: Solve for x
   x = 249.05/11.69
6. Step 6: Final answer
   x = 21.31