Question 1067052
I'm assuming that you mean blue pants or red shirt?
Because you didn't specify whether he had a blue shirt.
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He has a possibility of 
{{{N[tot]=3*5=15}}} pants/shirts combinations.
There are 5 blue pant/shirt combinations.
There are 3 pant/red shirt combinations.
There is 1 blue pant/red shirt combination.
That makes a total of 
{{{N=5+3-1=7}}}
So, blue pant or red shirt probability,
{{{P=7/15}}}