Thousands Black Jack

Lesson by Sophie Lurz
Quick lesson symbol
Download the PDF


Grade 5

  • Round whole numbers and decimals to the nearest ten, hundred, thousand, etc.
  • Students will use estimation when solving problems involving the addition, subtraction, multiplication, and division of whole numbers, to help judge the reasonableness of a solution. 


Educator playing with 4-5 students (at beginning) and as a whole class once all students are familiar with all the rules and mathematical concepts.  


  • Paper and pencil
  • Thousands Black Jack Math Card Game Cards that round to 100, 200, 300, 400, 500, 600, 700, 800,900,1000, and 1100 (4 of each)
  • Calculator


Similar to Black Jack, students have two cards and decide on whether they would like to hit or pass in order to be as close to 2100 as possible. Students are encouraged to round numbers and do estimations in their heads (mental math). Once all students have completed their estimations, all players will add their numbers and see who is the closest to 2100.


  • The dealer/educator deals out two cards to every student/player.
  • Players use mental math to round and estimate the sum of the two numbers. They can then either:
    • pass and not take another card
    • or hit and take more cards until they think they are as close to 2100 as they can get.
  • Once all students have completed their rounding and estimations, they can now use paper and pencil to calculate the exact sum.
  • The person with the closest sum to 2100 wins the game. 


  1. Review mathematical concepts such as rounding, adding, and determining the reasonability of sums together with students. Clear up any outstanding questions and/or misconceptions.
  2. Introduce and explain the objective and rules of the Thousands Black Jack. Ask students if they understand the game and provide the opportunity for students to ask questions. Clarify all misconceptions and explain in more detail if necessary. You may choose to play an example round. 
  3. Play the game in small groups. Ask students to share their thinking and strategies, as well as the estimated sum. 
  4. Once students have had the opportunity to calculate the exact sum on paper, allow them to use a calculator to check their estimates and prove their exact sum. Then use addition and subtraction to find the difference between the results to see who is closest to 2100. 
  5. Depending on the group’s level, introduce variations: play as a whole class, change the target number, etc.

Look Fors and Questions to Extend Student’s Thinking

  • What strategies do students use to ll up the space? Do they start off in the corners, the sides, or the middle of the space (spatial sense)? 
  • Is taking another card reasonable? Why or why not?
  • Did you round your cards up or down? Did that influence your decisions? If so, how?
  • An extension could be that instead of being as close to 2100 as possible, the students have to be as close to 2100 as possible without going over. This challenges students think more carefully about rounding before deciding whether to take another card. 
  • Same card game can be adapted to higher or lower sums, and even decimal sums, depending on curriculum expectations.
  • Are students able to successfully round numbers to the nearest tens, hundreds, thousands? Ask students to take notes on what they rounded up or down to. 
  • Are students able to complete all steps of the game? Do students use mental math successfully to determine the reasonability of their results? If not, which step is the student struggling with? Ask students to think out loud and share their thinking process. (Use a check mark assessment tool to ensure that students are rounding, estimating, and determine the reasonability).
  • Encourage students to reflect on the reasonability of their answer.