Finding the Third Proportional to 217.50 and 387.50

Step by Step Solution

1. Step 1: Write the proportion equation
   217.50 : 387.50 = 387.50 : x
2. Step 2: Convert to fraction form
   217.50/387.50 = 387.50/x
3. Step 3: Cross multiply
   217.50x = 387.50 × 387.50
4. Step 4: Simplify right side
   217.50x = 150,156.25
5. Step 5: Solve for x
   x = 150,156.25/217.50
6. Step 6: Final answer
   x = 690.37