Finding the Third Proportional to 640.72 and 1,379.69

Step by Step Solution

1. Step 1: Write the proportion equation
   640.72 : 1,379.69 = 1,379.69 : x
2. Step 2: Convert to fraction form
   640.72/1,379.69 = 1,379.69/x
3. Step 3: Cross multiply
   640.72x = 1,379.69 × 1,379.69
4. Step 4: Simplify right side
   640.72x = 1,903,542.99
5. Step 5: Solve for x
   x = 1,903,542.99/640.72
6. Step 6: Final answer
   x = 2,970.93