Finding the Third Proportional to 642.94 and 921.38

Step by Step Solution

1. Step 1: Write the proportion equation
   642.94 : 921.38 = 921.38 : x
2. Step 2: Convert to fraction form
   642.94/921.38 = 921.38/x
3. Step 3: Cross multiply
   642.94x = 921.38 × 921.38
4. Step 4: Simplify right side
   642.94x = 848,931.89
5. Step 5: Solve for x
   x = 848,931.89/642.94
6. Step 6: Final answer
   x = 1,320.40