Answer: The probability of being chosen by a wand made of holly or a wand made of dragon scale core is 0.4 or 40%
Step-by-step explanation: What we have are probabilities of two events. The first is the probability that Harry Potter is chosen by a wand made of Holly which is P(A). The other event is the probability that Harry is chosen by a wand with a dragon scale which is P(B).
In other to calculate P(A), there is a total of four possibilities, (that is holly, elm, maple and wenge). Therefore, the probability is derived as;
P(A) = Number of required outcomes/Number of all possible outcomes
P(A) = 1/4 or (0.25)
To calculate P(B), there is a total of five possibilities (that is phoenix feather, unicorn hair, dragon scale, raven feather and thestral tail). Therefore the probability is derived as;
P(B) = Number of required outcomes/Number of all possible outcomes
P(B) = 1/5 or (0.20)
However, the question requires the probability of P(A or B).
First we derive the probability of being chosen by a wand made of holly AND one made of a dragon scale core. In other words we shall calculate the probability of P(A and B) which is derived as;
P(A and B) = P(A) x P(B)
P(A and ) = 1/4 x 1/5
P(A and B) = 1/20 (0.05)
The probability of P(A or B) can now be calculated as follows;
P(A or B) = P(A) + P(B) - P(A and B)
P(A or B) = (0.25 +0.20) - 0.05
P(A or B) = 0.45 - 0.05
P(A or B) = 0.40
Therefore the probability that Harry Potter is chosen by a wand made of Holly or a wand with Dragon scale core is 0.4 or 40%