Finding the Third Proportional to 643.25 and 978.75

Step by Step Solution

1. Step 1: Write the proportion equation
   643.25 : 978.75 = 978.75 : x
2. Step 2: Convert to fraction form
   643.25/978.75 = 978.75/x
3. Step 3: Cross multiply
   643.25x = 978.75 × 978.75
4. Step 4: Simplify right side
   643.25x = 957,951.56
5. Step 5: Solve for x
   x = 957,951.56/643.25
6. Step 6: Final answer
   x = 1,489.24