Call the number of blue jays [tex]b[/tex] and the number of robins [tex]r[/tex]
We are told there are twice as may robins as blue jays: [tex]r=2b[/tex] and, there are 21 birds in total: [tex]r+b=21[/tex] thus, by substitution: [tex]2b+b=21[/tex] combine like terms: [tex]3b=21[/tex] solve for [tex]b[/tex]: [tex]b=7[/tex] back substitute: [tex]r=2(7)[/tex] [tex]r=14[/tex]
