Finding the Third Proportional to 687.69 and 1,621.78

Step by Step Solution

1. Step 1: Write the proportion equation
   687.69 : 1,621.78 = 1,621.78 : x
2. Step 2: Convert to fraction form
   687.69/1,621.78 = 1,621.78/x
3. Step 3: Cross multiply
   687.69x = 1,621.78 × 1,621.78
4. Step 4: Simplify right side
   687.69x = 2,630,174.42
5. Step 5: Solve for x
   x = 2,630,174.42/687.69
6. Step 6: Final answer
   x = 3,824.67