Finding the Third Proportional to 321.50 and 690.50

Step by Step Solution

1. Step 1: Write the proportion equation
   321.50 : 690.50 = 690.50 : x
2. Step 2: Convert to fraction form
   321.50/690.50 = 690.50/x
3. Step 3: Cross multiply
   321.50x = 690.50 × 690.50
4. Step 4: Simplify right side
   321.50x = 476,790.25
5. Step 5: Solve for x
   x = 476,790.25/321.50
6. Step 6: Final answer
   x = 1,483.02