How many fish are there? How many octopus?

Question

There are a total of 16 creatures, fish (with two fins) and octopus (with 8 tentacles). Altogether, there are 92 fins and tentacles. How many fish are there? How many octopus are there?

Answer 1

f + o = 16

2f + 8o = 92

The easiest way I see to solve is by substitution. First, solve the first equation for f or o. Let's do f.

f = 16 - o

Now, the = means whatever is on either side are the same, so we can substitute 16 - 0 for f in the 2nd equation.

2(16 - o) + 8o = 92

32 - 2o + 8o = 92

6o = 60

o = 10 octupus

f = 16 - o

f = 16 - 10

f = 6 fish