Answer :
x=# of cardinals
3 times as many robins as cardinals visited the feeder, so # of robins=3x
robins+cardinals=20, so x+3x=20
4x=20
x=5 cardinals
20-x=15 robins
3 times as many robins as cardinals visited the feeder, so # of robins=3x
robins+cardinals=20, so x+3x=20
4x=20
x=5 cardinals
20-x=15 robins
