I'm going to assume that the table looks like this:
Plants: 15 | 20
Fish: 6 | 8
If this is what it looks like, then the equation is:
2F=5P, or F=2.5P
When you have 3 plants, then you can substitute and solve:
2F=5P --> 2F=5(3) --Substitute
2F=5(3) --> 2F=15 --Multiply
2F=15 --> F=7.5 --Divide
The mathematical answer says 7.5 fish, but this answer might
be incorrect because we can clearly see that there are more plants than fish.
So, another method that you could use is to fill in the table:
Plants: 0 | 5 | 10 |15 | 20
Fish: 0 | 2 | 4 | 6 | 8
We can see from the table that when there are 0 plants, there are 0 fish,
and when there are 5 plants, there are 2 fish. We know that 3 is 3/5 of 5,
so we can use this ration to find 3/5 of 2, to find the number of fish in the
tank when there are 3 plants.
3/5 of 2 ends up being 1.2, but it's impossible to have 1.2 fishes (yes,
fishes is indeed a word), so you should round down to the nearest whole
fish.
The answer is 1.
