Guppies: u
Goldfish: o
3 times as many guppies as goldfish
3*o = u (there are more guppies than goldfish)
o + u = 20
o = 20 - u
Substitute in (20 - u) for o in the first equation and solve:
3* (20 - u) = u
60 - 3u = u
60 = 4u
u = 15
He has 15 guppies. Then substitute in the number of guppies into either equation to find the number of goldfish:
o + u = 20
o + (15) = 20
o = 5
Hope this helps! :)
