```
# import necessary libraries
import pandas as pd
import numpy as np
# define your series
s = pd.Series([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
# apply np.where() with condition
positions = np.where(s % 3 == 0)
# convert into series and print
result = pd.Series(positions[0])
print(f"Positions of Multiples of 3: \n{result}")
```