Finding the Third Proportional to 139.50 and 309.50

Step by Step Solution

1. Step 1: Write the proportion equation
   139.50 : 309.50 = 309.50 : x
2. Step 2: Convert to fraction form
   139.50/309.50 = 309.50/x
3. Step 3: Cross multiply
   139.50x = 309.50 × 309.50
4. Step 4: Simplify right side
   139.50x = 95,790.25
5. Step 5: Solve for x
   x = 95,790.25/139.50
6. Step 6: Final answer
   x = 686.67