Finding the Third Proportional to 287.72 and 390.66

Step by Step Solution

1. Step 1: Write the proportion equation
   287.72 : 390.66 = 390.66 : x
2. Step 2: Convert to fraction form
   287.72/390.66 = 390.66/x
3. Step 3: Cross multiply
   287.72x = 390.66 × 390.66
4. Step 4: Simplify right side
   287.72x = 152,612.31
5. Step 5: Solve for x
   x = 152,612.31/287.72
6. Step 6: Final answer
   x = 530.42