Atown has two shopping malls. a survey conducted on the shopping preferences of the town's residents showed that 62% of the residents visit comet mall, 73% of the residents visit star mall, and 48% of the residents visit both malls.
the probability that a resident chosen at random shops at either comet mall or at star mall is
%.

87%

To answer this question, you need to know how much % of resident that prefer Comet Mall and Star Mall separately. 

62% of the residents visit Comet Mall but 48% of them visit both malls, so only 14% resident visit Comet Mall only.
73% of the residents visit Star Mall but 48% of them visit both malls, so only 25% resident visit Star Mall only

Then, the chance would be:
%resident visit Comet Mall + % resident visit Star Mall + % resident visit both mall= 14%+25%+48%= 87%.