Finding the Third Proportional to 688.78 and 981.28

Step by Step Solution

1. Step 1: Write the proportion equation
   688.78 : 981.28 = 981.28 : x
2. Step 2: Convert to fraction form
   688.78/981.28 = 981.28/x
3. Step 3: Cross multiply
   688.78x = 981.28 × 981.28
4. Step 4: Simplify right side
   688.78x = 962,912.89
5. Step 5: Solve for x
   x = 962,912.89/688.78
6. Step 6: Final answer
   x = 1,398.00