Math Lesson Plan: Super Easy 9 Times Tables Trick

Objective:

1. Learn and remember the 9 times table (multiplication).

Materials:

1. Chartboard/marker  or blackboard/chalk
2. math journals

Method:

1. Print this statement on the board, “The sum of the product always equals 9, except 9X11, 9X21, 9X31, etc.”
2. Ask students what the hardest 9 times question is.  It’ll probably be 9X8 or 9X6.  Tell students you know a trick that will make it super easy to remember ALL the 9 times tables up to 9X10 in the next 5 minutes, and they don’t have to study flashcards.   Show them how the two digits add up to 9.  (eg. (9X8=72, 7 + 2 = 9…..9X6=54, 5 + 4=9)
3. The only trick then is figuring out what the first digit is.  Easy…it’s one less than the  second number (the multiplicand).  Example:  9 X 8 (so one less than 8 is …7 so…)  =  70 something,  and 7 + 2 =9  so the answer (product) is 72.I showed my grade 1 and 2 class this trick when we were talking about why it’s really important to be able to know all the combinations of 9, why we practised so often adding 2+7, 3+6, 4+5 etc. =9.  I told them that if you know the numbers that equal 9, you know the 9 times table in math.  They didn’t believe me so I taught them this trick and they all went home that day knowing quite a lot of the 9 times table !!!   They loved it!!!
4. This is where I got students to just say 20 something or 30 something for the answers.   9X6 = 50 something.  9X8 = 70 something.  9X5 = 40 something.  Do a few more like that.  Once they had mastered figuring out the first digit, I added the second step…  figuring out what the second number was that added up to 9.
5. After a bit of practise with #4 above, try another question and see if the students “get it”.  9 X 7 = 60 something, and 6 + 3 = 9  so the answer is 63.
6. Try a hard one now.  See how quickly hands go up.  9X8 = __   (I tell them to answer with the first digit, even if they don’t immediately know the second digit….so they say “seventy…..” then in their head they figure out they need a two, then continue with “…..two”.  )  This way they answer immediately and get quicker and quicker with the answers.

THESE ARE SLIGHTLY HARDER:

1. It even works for 9 X 12 = 108 (the two digits in the answer add up to 9, but you can’t go one less than the multiplicand to find the first digit of the answer).
2. In 9 X 13 = 117, the answer digits add up to 9, but you have to know the answer is over 100.  (9 X 10 is 90 and 9 X 3 is 27, so 90 and 27 is over 100.  This is another good way to show students how to use regrouping to figure out answers as well.)
3. In 9 X 14 = 1_6….the missing digit is 2.  Students know that 9 X10 is 90 so you need over 9X20 to get close to 200, so students know the answer is still at least 100.  They now know that 9 X 4 is 36, and….(solving for the answer) 1 + 6 is 7….they need to total 9 (for the three digits in the product)….so the 2 is missing (=126)…..9X14= 126.   Just knowing 9 X 4 = 36 will help students “regroup” the 3 with the 9 to get “12” to get “126”.  It’s another way to look at solving these problems that might be easier for that one student to grasp.EXCEPTIONS:  9X11, 9X21, 9X31, 9X41, etc.
4. Write in math journals:  Multiplying by 9:  The sum of the product always equals 9, except 9X11, 9X21, 9X31, etc.  Examples: 9 X 3 = 27 (2 plus 7 =9)

Tags: multiplication, multiplying X9 trick