Answer: 60
Step-by-step explanation:
let x="students enrolled in all three"
"170 are enrolled in both Math and English" __ so 170-x are enrolled in ONLY Math and English
"150 are enrolled in both History and English" __ so 150-x are enrolled in ONLY History and English
"300 are enrolled in Math and History" __ so 300-x are enrolled in ONLY Math and History
"500 students are enrolled in at least two of these three classes"
so (170-x)+(150-x)+(300-x)+x = 500
620-2x=500
120=2x
60=x