If Benito had 10 days of vacation, then:
1/5 of this time is 20%
Soccer camp is 30%
10 days are 100%, so if he spent 20% of his time fishing and 30% at soccer camp, then he spent 50% at the beach:
100% - (20% + 30%) = 100% - 50% = 50%
Answer: Benito spend 50% of his vacation at the beach.