Finding the Third Proportional to 679.78 and 991.69

Step by Step Solution

1. Step 1: Write the proportion equation
   679.78 : 991.69 = 991.69 : x
2. Step 2: Convert to fraction form
   679.78/991.69 = 991.69/x
3. Step 3: Cross multiply
   679.78x = 991.69 × 991.69
4. Step 4: Simplify right side
   679.78x = 983,444.10
5. Step 5: Solve for x
   x = 983,444.10/679.78
6. Step 6: Final answer
   x = 1,446.71