Answer :
[tex]12+5+10+3=30[/tex] <-- the number of all keys
[tex]12+10=22[/tex] <-- the number of silver and copper keys
The probability is [tex]\frac{22}{30}=\frac{11}{15}[/tex]
[tex]12+10=22[/tex] <-- the number of silver and copper keys
The probability is [tex]\frac{22}{30}=\frac{11}{15}[/tex]