Finding the Third Proportional to 255.81 and 405.69

Step by Step Solution

1. Step 1: Write the proportion equation
   255.81 : 405.69 = 405.69 : x
2. Step 2: Convert to fraction form
   255.81/405.69 = 405.69/x
3. Step 3: Cross multiply
   255.81x = 405.69 × 405.69
4. Step 4: Simplify right side
   255.81x = 164,582.35
5. Step 5: Solve for x
   x = 164,582.35/255.81
6. Step 6: Final answer
   x = 643.37