Lesson: Addition Speed Tricks

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Lesson Objective

SWBAT use multiple strategies when adding numbers.

Lesson Plan

Building Number Sense (5 minutes)

Take the day of school and build it with different coin sets, if its 25 you could build it with two dimes one nickel, five nickels, four nickels five pennies, twenty five pennies. Stress the changing in counting with each coin, nickels are by fives, pennies are by ones, dimes are by tens. Then count out each student suggested combination with the class to check them. Discuss which combination of coins the students would use and why.


 

Name Collection Box (Use the number from the day of school, write number in top left of box, write different “names” for that number in box; coins, base ten blocks, tallies, pictures, words, etc.)

Mental Math Fluency (5 minutes)

Pepper with addition facts (all students stand, ask each student an addition problem, when student answers correctly they sit and “earn their seat”)


 

Problem of the Day  (7 minutes)

Teacher (T): For today’s problem of the day make sure you use one of our addition strategies.

(For today’s problem of the day cover the problem somehow with a piece of paper, or flip it over, etc.)

T: For today’s problem of the day our focus is speed again. So I am going to flip this chart paper over and there will be a word problem on the other side, when you know the answer raise your hand. [Flip over chart]

Jonathon had 6 tennis balls, Areyanna had 10 tennis balls, how many did they have altogether?

T: [Call on first hand]

Student (S): 13

T: How did you solve this problem?

S: I counted on my finger, I counted in my head, I drew a picture, OR I added 6+6 which I know is 12 then I added 1.

T: Well I’m here to tell you that doubles facts are not the only tricks we are going to have in our math toolbox, today we are going to learn a lot of tricks and you’ll get to pick some that are your favorite and even get to make up your own if you get inspired.


 

Mini Lesson              (12 minutes)

(With all questions you may elicit answers from class or give answer depending on time, class, and teaching style. I prefer to have kids drive answers and all the answers written are the conclusions I will drive student conversations to. But I still keep it very teacher driven as this is the “I” do)

T: Remember our math problems are like puzzles and almost all of them have a special key that make them easy to solve. Our problem of the day has such a key. This key just like yesterday is a mental math key. I love mental math keys because they make math quick and fun. I’m going to write up a couple of facts and let’s see if you can come up with the trick. [write 10+1=11, 10+3=13, 10+4=14, 10+5=15, 10+6=16, 10+7=17] Does anyone see any patterns? Any ideas on what our trick could be?

Teacher or Student (TS): we add the single digit number to the ones place OR we drop the zero and add the single digit number to the 1 in the tens place, etc.

T: Exactly whenever we are adding a single digit number to 10 all we need to do is drop the 0 and add the single digit number into the ones place. Now let’s see if you can find the trick to these (9+2=11, 9+3=12, 9+4=13, etc.)

TS: We take one away from the number next to the nine and put a one in front (i.e. 9+6=, you take 5 and put a one in front 15), it’s just like 10 plus the number that is not nine but then take away one, etc.

T: Great, when we see 9 plus a number we just take one away from the number and add a one in front (or you can say make that number minus one a “teen” nine plus five is FOUR-teen). I really love these tricks it’s so fun figuring out the puzzle and finding the right key to unlock the answer. Now can you figure out some patterns on your own? What if we are adding a 1 to a number? What about adding two? What if we are adding to 11? Do some work on your paper and see if you can find some numbers (I purposely left +1 and +2 until now so they can have these easy “tricks” to find and then feel confident to find harder tricks)

Give students time to explore some numbers, walk around and push their thinking towards some tricks, have them partner share the tricks they have, have them share them with the class on the whiteboard or chart paper, etc.

Some examples:

A number +1 is just like counting and you just count up one more number.

A number +2 is just like counting by twos, or you just have to count up twice.

11 plus a single digit number below 9 you just add one to that number then make it a teen (11+7, you add one to seven and get 8 then make it a teen 18)

A 0 or 5 in the ones place plus 5 is just like counting by 5’s (10+5=15)

A 0 in the ones place plus 10 is just like counting by 10’s

A tens (10, 20, 30, 40) plus a single digit number is just like the tens trick, you drop the ones place and add the single digit (20+9=29)


 

Work Time (Zones, Independent, Group 30 minutes)

Group Work “You Do” (Math Zones): Play through a couple of rounds of this game with the students, you vs. the class, so that they get down the procedures.

 Play domino train. In groups of four students put dominoes face down, student one draws a domino and makes the fact on it (if the domino is a 9 and a 7 then they write 9+7) then tries to write down/share verbally a trick to solve it, once it is solved player one puts the domino in the middle of the table. The next player draws a domino and solves trying to find a trick, then if their domino matches one of the numbers on the domino in the middle (if it is a 7 and a 3 then it would match the 7 on the first domino) they can add it to the domino train, if there domino doesn’t match the 7 or the 9 then they keep it in there bank and play it on a later turn if one of the two ends of the domino train have a number of one of their dominoes in their bank. (to make it more difficult/accountable you can say that the only way they get to play the domino is if they come up with a trick and write it down, if they don’t they have to put the domino back face down, so if they draw a domino that is 6+6= they could write under that “doubles” if they get a domino that is 8+9= they could write 8+8= 16 16+1=17).


 

Math Reflection/Share (4 minutes)

(This is a time to share work and discuss critically a problem a student had or explain student work. Also this time can be used to ask a difficult question that takes the concept taught one more level up in bloom’s taxonomy)

What is your favorite trick? Explain why it is your favorite trick, and if you can write down three different equations you could use the trick on.

Example: My favorite trick is the 10 plus a single digit, where you just replace the 0 with the single digit number, because it is really easy to just drop the ones digit and add the single digit number, also I get to use the trick with 20 or 30 or 40, all of the tens!

10+4=14  50+6= 56    10+9=19


 

1. What went well?

2. What would you change?

3. What needs explanation?

Leaving the plus one and plus two pattern for the students to find and explain eased some students into creating their own “tricks”  that wouldn’t have tried normally, thinking it would be too hard to find patterns in addition sentences.

It would have been cool to have some cut out keys before the lesson and be writing down the tricks we found and then add them to a poster on the wall entitled “Unlocking Addition Sentences”. It would have been exciting and engage them to strive more to find patterns of their own. I will do this tomorrow probably.

These are math tricks which I have used in my head since middle school, they are not “standard” or nationally recognized. That being said think of some math tricks you use and add them to the list, also be very open to students ideas, this is a great lesson to really build a culture of putting ideas out there, increasing math talk, playing with math, and feeling ok with things being hard or getting things wrong. Be explicit that these tricks are created not given and students will find some tricks they like and some they don’t.

Lesson Resources

Math Unit 2 Day 5  
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Math Unit 2 Day 5 Worksheet   Classwork
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