Full Length Lesson Plans from an Elementary School Teacher
Math Lesson Plan: Super Easy 9 Times Tables Trick
- Learn and remember the 9 times table (multiplication).
- Chartboard/marker or blackboard/chalk
- math journals
- Print this statement on the board, “The sum of the product always equals 9, except 9X11, 9X21, 9X31, etc.”
- 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)
- 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!!!
- 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.
- 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.
- 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:
- 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).
- 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.)
- 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.
- 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)