Ross collects lizards, beetles and worms. He has more worms then lizards and beetles together. Altogether in the collection there are 31 heads and 78 legs. How many lizards does Ross have?

7 worms, 3 beetles, 2 lizards

I found this by first doing the calculations for the number of legs (26). First, I added the legs for the 3 beetles together to get 18 legs. Then I added the legs for 2 lizards (8) to the beetles’ legs to get 26 legs in total. To find the number of heads I added the number of lizard heads (2) and beetles heads (3) to get five heads. Then I added the 7 worm’s heads to the lizard and beetles heads to get 12 heads in total.