Finding the Third Proportional to 312.56 and 399.56

Step by Step Solution

1. Step 1: Write the proportion equation
   312.56 : 399.56 = 399.56 : x
2. Step 2: Convert to fraction form
   312.56/399.56 = 399.56/x
3. Step 3: Cross multiply
   312.56x = 399.56 × 399.56
4. Step 4: Simplify right side
   312.56x = 159,650.19
5. Step 5: Solve for x
   x = 159,650.19/312.56
6. Step 6: Final answer
   x = 510.78