Given that the total number of swimmers is 80, and the ratio of the seventh grade swimmers to all swimmers is 5:16. You will know that answer for this through cross multiplication. So let's put it this way:
5 ?
-- ----
16 80
Multiply 80 by 5 and you get 400 then divide this by 16 and you get 25.
Therefore, out of 80 swimmers, there are 25 seventh grade swimmers. Hope this answer helps.
