Finding the Third Proportional to 318.78 and 488.69

Step by Step Solution

1. Step 1: Write the proportion equation
   318.78 : 488.69 = 488.69 : x
2. Step 2: Convert to fraction form
   318.78/488.69 = 488.69/x
3. Step 3: Cross multiply
   318.78x = 488.69 × 488.69
4. Step 4: Simplify right side
   318.78x = 238,817.38
5. Step 5: Solve for x
   x = 238,817.38/318.78
6. Step 6: Final answer
   x = 749.16