Grade
4

Math in Our World: Hermit Crab Tank

Huong has a hermit crab tank that is 75 centimeters long and 30 centimeters wide.

He has $30 to spend on some accessories.

Huong wants to make sure he has space in his tank for the crab to climb, and for food and water. He also wants the tank to look cool.

He wanted to make sure all of the accessories he bought would fit on the bottom of the tank, so he looked at the dimensions (length and width) of each item.

A table shows a picture, the dimensions, and the price of each accessory Huong is considering. Climbing branch: 16 cm by 5 cm, $5. Lagoon/water dish: 8 cm by 10 cm, $4. Food dish: 12 cm by 10 cm, $5. Cave: 23 cm by 40 cm, $9. Palm tree: 5 cm by 15 cm, $7. Starfish decoration: 6 cm by 6 cm, $3. Mini castle: 14 cm by 25 cm, $12.
  • Use pictures, models, or numbers to show what you know about the situation.
  • What do you notice? What do you wonder?
  • What mathematical questions can you ask about this situation? Answer all the questions you can!
  • Find the area of the tank.
  • Find the area of the base of each of the items that Huong might want to put in the tank.
  • Use grid paper to draw a picture of the base of the tank and show how you would place each item.
  • Show your work to someone else, and explain your thinking. Did they understand?
  • Ask whether they have any other questions you can answer!

Think of a pet that you might want to get. Think about how big the enclosure would have to be and what things you might want to put inside.

Printable Version

Google doc for printing and copying

Seesaw Version

Activity for the Seesaw platform

Reference for Educators

Sample problems and solutions