Finding the Third Proportional to 256.78 and 387.42

Step by Step Solution

1. Step 1: Write the proportion equation
   256.78 : 387.42 = 387.42 : x
2. Step 2: Convert to fraction form
   256.78/387.42 = 387.42/x
3. Step 3: Cross multiply
   256.78x = 387.42 × 387.42
4. Step 4: Simplify right side
   256.78x = 150,095.71
5. Step 5: Solve for x
   x = 150,095.71/256.78
6. Step 6: Final answer
   x = 584.53