Finding the Third Proportional to 391.50 and 813.38

Step by Step Solution

1. Step 1: Write the proportion equation
   391.50 : 813.38 = 813.38 : x
2. Step 2: Convert to fraction form
   391.50/813.38 = 813.38/x
3. Step 3: Cross multiply
   391.50x = 813.38 × 813.38
4. Step 4: Simplify right side
   391.50x = 661,578.89
5. Step 5: Solve for x
   x = 661,578.89/391.50
6. Step 6: Final answer
   x = 1,689.86