The probability that he or she has a basic model is 28.57%.
This situation required conditional probability using this formula
P(B|E) = P(B∩E) ÷ P(E)
P(B|E) is the probability of he or she only have basic model, if he or she bought extended warranty.
P(B∩E) is the probability of he or she have basic model and extended warranty.
P(E) is the probability of he or she bought extended warranty.
First, calculate P(B∩E)
P(B∩E) = 0.4 × 0.3
= 0.12
Next, calculate P(E)
P(E) = 0.4 × 0.3 + 0.6 × 0.5
= 0.12 + 0.3
= 0.42
Then, put P(B∩E) and P(E) to formula
P(B|E) = 0.12 ÷ 0.42
= 0.2857 or 28.57%
Thus, there is a 28.57% chance that he or she has a basic model.
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