Finding the Third Proportional to 639.25 and 978.50

Step by Step Solution

1. Step 1: Write the proportion equation
   639.25 : 978.50 = 978.50 : x
2. Step 2: Convert to fraction form
   639.25/978.50 = 978.50/x
3. Step 3: Cross multiply
   639.25x = 978.50 × 978.50
4. Step 4: Simplify right side
   639.25x = 957,462.25
5. Step 5: Solve for x
   x = 957,462.25/639.25
6. Step 6: Final answer
   x = 1,497.79