Finding the Third Proportional to 666.56 and 679.50

Step by Step Solution

1. Step 1: Write the proportion equation
   666.56 : 679.50 = 679.50 : x
2. Step 2: Convert to fraction form
   666.56/679.50 = 679.50/x
3. Step 3: Cross multiply
   666.56x = 679.50 × 679.50
4. Step 4: Simplify right side
   666.56x = 461,720.25
5. Step 5: Solve for x
   x = 461,720.25/666.56
6. Step 6: Final answer
   x = 692.69