Ken spent 1/5 of his allowance on a movie, 3/8 on snacks, and 2/7 on games. If his allowance was $20, how much did Ken have left?

1/5 of 20 is $4. So, 20-4=$16 remaining.
3/8 of 16 is $7.50. So, 16-7.50= $8.50 remaining.
2/7 of 8.5 is $2.43. So, 8.50-2.43 is $6.07

Answer: Ken has $6.07 left after all his purchases.