Math in Our World: Trip to the Aquarium

In this aquarium tank there are sea stars with 5 arms each, and squid with 10 arms each. Gina counted 50 arms in all.

Gina went to the aquarium yesterday.
She learned that some sea animals have arms.

One of the tanks had sea stars and squid in it.
Gina counted 50 arms in the tank. Wow, that’s a lot of arms!

  1. What do you notice? What do you wonder?
  2. Show or tell what you know about the arms in the tank. Use pictures, numbers, symbols, or math words.
  3. What math questions can you ask about the sea stars and squid in the tank? Answer all the questions you can!
  • Think about how many sea stars and squid it takes to make 50 arms in all.
    Remember, each sea star has 5 arms and each squid has 10 arms.
    There’s more than one right answer!
  • You might start at 0 and count by 10s and 5s to get to 50.
    Count 10 for each squid in the tank. Count 5 for each sea star.
  • If it helps, draw simple pictures to help you keep track of the total number of arms.
  • Show your work to someone and explain your thinking. Did they understand?
  • Ask whether they have any other questions you can answer!

Choose two kinds of animals and write a story problem about their legs.
Can you include 12 or more legs in your story problem?
We’d love to see what you write, so share your problem with us!

Here are some facts about legs to get you started. It’s okay to use other animals, too!

People usually have 2 legs. Dogs usually have 4 legs. Ladybugs usually have 6 legs. Spiders usually have 8 legs.