Finding the Third Proportional to 311.38 and 421.38

Step by Step Solution

1. Step 1: Write the proportion equation
   311.38 : 421.38 = 421.38 : x
2. Step 2: Convert to fraction form
   311.38/421.38 = 421.38/x
3. Step 3: Cross multiply
   311.38x = 421.38 × 421.38
4. Step 4: Simplify right side
   311.38x = 177,556.89
5. Step 5: Solve for x
   x = 177,556.89/311.38
6. Step 6: Final answer
   x = 570.23