Finding the Third Proportional to 687.75 and 978.75

Step by Step Solution

1. Step 1: Write the proportion equation
   687.75 : 978.75 = 978.75 : x
2. Step 2: Convert to fraction form
   687.75/978.75 = 978.75/x
3. Step 3: Cross multiply
   687.75x = 978.75 × 978.75
4. Step 4: Simplify right side
   687.75x = 957,951.56
5. Step 5: Solve for x
   x = 957,951.56/687.75
6. Step 6: Final answer
   x = 1,392.88