If Pr(A) = 4 Pr(B), $\displaystyle Pr(A\cup B) =0.8$ and $\displaystyle Pr(A\cap B) = 0.2$, find:

a) Pr(B)

b) Pr(A)

The bit that confuses me most was probably "Pr(A) = 4 Pr(B)" in the question above. Is this a typo? I've tried figuring this out for few times but I keep getting negative numbers.

Any help would be appreciated.