Finding the Third Proportional to 679.78 and 917.72

Step by Step Solution

1. Step 1: Write the proportion equation
   679.78 : 917.72 = 917.72 : x
2. Step 2: Convert to fraction form
   679.78/917.72 = 917.72/x
3. Step 3: Cross multiply
   679.78x = 917.72 × 917.72
4. Step 4: Simplify right side
   679.78x = 842,207.70
5. Step 5: Solve for x
   x = 842,207.70/679.78
6. Step 6: Final answer
   x = 1,238.94