Question

three times as many robins as cardinals visited a bird feeder. if a total of 20 robins and cardinals visited the feeder, how many were robins?

Answer 1

3c = r
c + r = 20
sub the 3c in for r in the 2nd equation
c + (3c) = 20 -- now combine like terms
4c = 20 -- now divide by 4 to get c by itself
4c/4 = 20/4
c = 5
now sub 5 in for c in either of the equations
3c = r
3(5) = r
15 = r
check...
c + r = 20
5 + 15 = 20
20 = 20 (correct)
There were 15 robins and 5 cardinals.

Answer 2

Do you have any questions....if so....please ask and I can explain what I did.

Answer 3

@texaschick101 The idea on OS is to help people learn not to simply do their problems for them.
Give a man a fish and you feed him for a day, teach a man to fish and you feed him for life.