I made a probability tree. Pls. see attachment.
Based on the probability tree I made, below are the probabilities
Probability of a student accepted at both Dartmouth and Harvard is:
50% x 40% = 20%
Probability of a student accepted at Dartmouth but not Harvard is:
50% x 60% = 30%
Probability of a student not accepted at Dartmouth but accepted in Harvard is:
50% x 20% = 10%
Probability of a student not accepted in both schools is:
50% x 80% = 40%
As you can see, these probabilities total 100%