Finding the Third Proportional to 405.50 and 815.50

Step by Step Solution

1. Step 1: Write the proportion equation
   405.50 : 815.50 = 815.50 : x
2. Step 2: Convert to fraction form
   405.50/815.50 = 815.50/x
3. Step 3: Cross multiply
   405.50x = 815.50 × 815.50
4. Step 4: Simplify right side
   405.50x = 665,040.25
5. Step 5: Solve for x
   x = 665,040.25/405.50
6. Step 6: Final answer
   x = 1,640.05