Probability of college acceptance
Assuming the college decisions are independent of each other (which is not true in real life but we simplify the problem)
The probability at least one college accepts you is $1-P(\text{no accept})$ which is $$ 1-\left(.2\right)^3 = .992 $$
The chance that exactly one college accepts you is $3$ times the probability one takes you times the probability that the other decline you. We multiply by $3$ to signify that any of the $3$ could accept us $$ 3(.8)(.2)^2 = .096 $$