Finding the Third Proportional to 427.78 and 688.78

Step by Step Solution

1. Step 1: Write the proportion equation
   427.78 : 688.78 = 688.78 : x
2. Step 2: Convert to fraction form
   427.78/688.78 = 688.78/x
3. Step 3: Cross multiply
   427.78x = 688.78 × 688.78
4. Step 4: Simplify right side
   427.78x = 474,419.61
5. Step 5: Solve for x
   x = 474,419.61/427.78
6. Step 6: Final answer
   x = 1,109.02