Finding the Third Proportional to 128.50 and 317.50

Step by Step Solution

1. Step 1: Write the proportion equation
   128.50 : 317.50 = 317.50 : x
2. Step 2: Convert to fraction form
   128.50/317.50 = 317.50/x
3. Step 3: Cross multiply
   128.50x = 317.50 × 317.50
4. Step 4: Simplify right side
   128.50x = 100,806.25
5. Step 5: Solve for x
   x = 100,806.25/128.50
6. Step 6: Final answer
   x = 784.48