Finding the Third Proportional to 222.13 and 390.88

Step by Step Solution

1. Step 1: Write the proportion equation
   222.13 : 390.88 = 390.88 : x
2. Step 2: Convert to fraction form
   222.13/390.88 = 390.88/x
3. Step 3: Cross multiply
   222.13x = 390.88 × 390.88
4. Step 4: Simplify right side
   222.13x = 152,783.27
5. Step 5: Solve for x
   x = 152,783.27/222.13
6. Step 6: Final answer
   x = 687.83