Finding the Third Proportional to 278.69 and 431.31

Step by Step Solution

1. Step 1: Write the proportion equation
   278.69 : 431.31 = 431.31 : x
2. Step 2: Convert to fraction form
   278.69/431.31 = 431.31/x
3. Step 3: Cross multiply
   278.69x = 431.31 × 431.31
4. Step 4: Simplify right side
   278.69x = 186,030.47
5. Step 5: Solve for x
   x = 186,030.47/278.69
6. Step 6: Final answer
   x = 667.52