Answer:
[tex]\frac{10}{11}[/tex]
Step-by-step explanation:
Note : the total number of students is 55
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[tex]p\left( A\cup B\right) =p\left( A\right) +p\left( B\right) -p\left( A\cap B\right)[/tex]
p(A) = 40/55
p(B) = 15/55
[tex]p\left( A\cap B\right) =\frac{5}{55}[/tex]
Therefore,
[tex]p\left( A\cup B\right) =p\left( A\right) +p\left( B\right) -p\left( A\cap B\right)[/tex]
        [tex]=\frac{40}{55} +\frac{15}{55} -\frac{5}{55}[/tex]
        [tex]=\frac{50}{55}[/tex]
        [tex]=\frac{10}{11}[/tex]
