Finding the Fourth Proportional to 139.50, 209.31 and 82.50

Step by Step Solution

1. Step 1: Write the proportion equation
   139.50 : 209.31 = 82.50 : x
2. Step 2: Convert to fraction form
   139.50/209.31 = 82.50/x
3. Step 3: Cross multiply
   139.50x = 209.31 × 82.50
4. Step 4: Simplify right side
   139.50x = 17,268.08
5. Step 5: Solve for x
   x = 17,268.08/139.50
6. Step 6: Final answer
   x = 123.79