Finding the Third Proportional to 139.69 and 209.81

Step by Step Solution

1. Step 1: Write the proportion equation
   139.69 : 209.81 = 209.81 : x
2. Step 2: Convert to fraction form
   139.69/209.81 = 209.81/x
3. Step 3: Cross multiply
   139.69x = 209.81 × 209.81
4. Step 4: Simplify right side
   139.69x = 44,021.29
5. Step 5: Solve for x
   x = 44,021.29/139.69
6. Step 6: Final answer
   x = 315.14