Help with this probability question please

Half the population of green village is vegetarians, and 35% ride bicycles. If 20% are both vegetarian and ride bicycles, what is the probability that a person chosen at random from green village is either a vegetarian or rides a bicycle?

explain please. Thanks.

If you mean or in the sense one event or both happen :
(1) P[A or B] = P[A] + P[B] - P[A and B]
If you mean with either ... or.. , exclusive or : exactly one event happens :
(2) P[A xor B] = P[A or B] - P[A and B]

(1) = 0.5 + 0.35 - 0.2 = 0.65
(2) = 0.65 - 0.2 = 0.45

So we have 65 % for the or-case and 45 % for the exclusive or-case

Population = P
Veggies = 0.5P
Bikers = 0.35P
Veggie Bikers = 0.20P
There are 0.50-.20 = 0.30 veggies Only
There are 0.35-.20 = 0.15 Bikers Only
So You have a 45% chance (0.30+0.15) of choosing a vegan only or a biker only.

Let A = vegetarian
B = rides a bicycle

P(A) = 0.50
P(B) = 0.25
P( A and B) = 0.20

P(A or B) = P(A)+P(B)-P(A and B) ---- this is a formula
P(A or B) = 0.50+0.35-0.20
= 0.65