Finding the Third Proportional to 639.50 and 1,345

Step by Step Solution

1. Step 1: Write the proportion equation
   639.50 : 1,345 = 1,345 : x
2. Step 2: Convert to fraction form
   639.50/1,345 = 1,345/x
3. Step 3: Cross multiply
   639.50x = 1,345 × 1,345
4. Step 4: Simplify right side
   639.50x = 1,809,025
5. Step 5: Solve for x
   x = 1,809,025/639.50
6. Step 6: Final answer
   x = 2,828.81