Answer:
He left with $2.786.
Explanation:
Consider the provided information.
Ken spent 1/5 of his allowance on a movie, 3/8 on snacks, and 2/7 on games.
It is given that his allowance was $20.
The money spent on movie is:

He spent $4 for movie.
The money spent on snacks is:

He spent $7.5 for movie.
The money spent on games is:

He spent $5.714 for movie.
Subtract the money spent from total allowance as shown:

Hence, he left with $2.786.