Kiss those Math Headaches GOODBYE!

Posts tagged ‘Math Facts’

Multiplication Trick #1 — Fun with the 5s


 

SPICE IT UP!

That’s my advice to teachers and parents who see students getting bored or frustrated as they try to learn their times tables. 

As you help students learn these critical facts, it helps, from time to time — to work on multiplication in a fun and relaxing way.

This is the first in a series of blogposts that make it more pleasurable to learn multiplication facts — by teaching multiplication tricks. Each post will contain a complete lesson plan:  instruction, practice problems, and all answers. 

The first such trick is for multiplying by 5.

TRICK #1:


WHAT THE TRICK LETS YOU DO:
  Multiply numbers by 5.


HOW YOU DO IT (EVEN NUMBERS):
When multiplying an even number by 5, just take half the value of the even number, then put 0 at the end.  Ta da … that’s your answer.

 

Example:  5 x 14

Half of 14 is 7.

Put down the 7, then put a 0 after it, and you get 70.

That’s the answer:  5 x 14 = 70.

Can you believe that it’s that easy? Watch how you can do the same feat with larger numbers…

 

Another example:  5 x 48

Half of 48 is 24.

Put down the 24, then put a 0 after it, and you get 240.

That’s the answer:  5 x 48 = 240.

 

PRACTICE Set A:  (Answers at bottom)

5 x 8

5 x 16

5 x 4

5 x 28

5 x 36

5 x 84

5 x 468


HOW YOU DO IT (ODD NUMBERS):
When multiplying an odd number by 5, first subtract 1 from the odd number, thus making it an even number. Then use the trick (above) for even numbers. And here’s the new thing to know — instead of putting a 0 after the result, put a 5.


Example:  5 x 13

13 – 1 = 12

Half of 12 is 6.

Put down the 6, then put a 5 after it, and you get 65, That’s the answer:

5 x 13 = 65.

 

Another example: 5 x 29


29 – 1 = 28

Half of 28 is 14.

Put down the 14, then put a 5 after it, and you get 145. That’s the answer:

5 x 29 = 145.

 

PRACTICE Set B:  (Answers at bottom)

5 x 7

5 x 13

5 x 9

5 x 15

5 x 23

5 x 47

5 x 685

 

ANSWERS Set A: 

5 x 8  = 40

5 x 16  = 80

5 x 4  =  20

5 x 28  =  140

5 x 36  =  180

5 x 84  =  420

5 x 468  =  2,340

 

 

ANSWERS Set B: 

5 x 7  =  35

5 x 13  =  65

5 x 9  =  45

5 x 15  =  75

5 x 23  =  115

5 x 47  =  235

5 x 685  =  3,425

 

 


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Multiplication Facts


QUESTION:

Is there a particular order that is most beneficial to learning times tables? For example, I have heard that learning 1, 5, 10, 11, 2, 4, 8, 12, 3, 6, 9 is a good order. What say you?

MY REPLY:

There are many “schools of thought” on what makes the best order for teaching the times tables.

I encourage everyone out there who has a favorite order to share it with us in the comments. And feel free to explain why this is your favorite order.

Here is my preferred order — and a few notes on why:

1, 2, 4, 10, 5, 11, 3, 6, 9, 8, 12, 7

IMPORTANT NOTE: I teach the facts for the multiplicands 1 – 6 first. Only after
students have those down do I advance to the multiplicands of 7 – 12.

i.e.: When teaching the x 4 facts the first round through, teach 1 x 4 through 6 x 4. On the second round through, teach the 7s through 12s, i.e.: 7 x 4 through 12 x 4.

Using this staggered approach helps students avoid getting befuddled by the size of numbers they encounter early on. This approach builds success and confidence early on.

A few notes on my order:

1st) I teach x 2 second. That’s because you can teach multiplying by 2 as simply “doubling” the number, a concept almost all kids understand. The “doubling” approach gives teachers a good way to talk if you’re going to use manipulatives to reinforce the concept.

In suggesting that you use manipulatives, I mean that you may want to use counters such as tiddly winks, paper clips, pennies, etc. To demonstrate a fact like 2 x 7, you would first lay out a row of 7 counters, then underneath them put out another row of 7 counters, and you would have the student count them all up.

2nd) I put x 4 third because you can teach multiplying by 4 as doubling a number TWICE. e.g.,: 4 x 3: 3 doubled is 6. And 6 doubled is 12, so 4 x 3 = 12.

Again, it would be a good idea to use manipulative counters to demonstrate this concept. Here you would lay out four rows of three counters, to show the fact that 4 x 3 = 12

3rd) I teach x 5 right after x 10 because multiplying by 5 gives you a number that’s exactly half of what you get when you multiply by 10.

When teaching the 5s tables, use the trick that multiplying by 5 is the same as multiplying by 10 and cutting in half. (And, for even multiples of 5, first cutting the number in half, then tacking on a 0 at the end.)

e.g.: for 4 x 5: Half of 4 is 2. Tack on a 0, and you get 20 4 x 5 = 20 [yes, it is that easy!]

4th) You can teach multiplying by 8 in several ways, depending on what works for your children. One way is to see that multiplying by 8 is doubling a number three times. e.g., for 6 x 8: 6 doubled is 12. 12 doubled is 24. 24 doubled is 48. So 6 x 8 = 48

Another strategy for 8: Multiply by 10, then take away 2 x the number. e.g., for 6 x 8: 10 x 6 = 60, and 2 x 6 = 12. 60 – 12 = 48, so 6 x 8 = 48

5th) Multiplying by 12 offers you a great chance to introduce the distributive property for multiplication. That’s just fancy language for saying that when you multiply, say, 6 x 12, you can look at it like this: Since 12 = 10 + 2, 6 x 12 can be viewed as: (6 x 10) + (6 x 2) = 60 + 12 = 72

Most children can get used to this quickly, if they are taught it EARLY ENOUGH.

Exploring Addition Facts


QUESTION:

I have been asked to help my grandson memorize the addition tables. If I ask him what is 8 + 5, I watch him doing it in his head. He gets the right answer but takes a long time, which may hurt him later when he is introduced to multiplication. Do you have any suggestions?

MY REPLY:

Great question.

Without knowing your grandson, it’s impossible to know what he is doing when he takes some time to figure out addition facts.

But I’d suggest is that you just ask him — in a happy and curious way — what thought steps he is going through.

You can tell him that you’ve heard that students do mental math in different ways, and that you’d be interested to know how he is doing it. You might also want to reassure him that there is no “wrong” way to do math in your head.

[Be aware: some children have trouble verbalizing what they’re “doing” when they do math mentally. If your grandson has trouble telling you, you might prompt him by asking if he’s using either of the strategies I describe below.]

It may be that your grandson is trying to retrieve a memorized fact, but it’s more likely that he is using some kind of mental operation to arrive at the answer.

For example, it may be that he is “counting up” 5 from 8, to get to the answer. (If so, it would be commendable that he can count up 5 in his head — without using his fingers. Not all students can do this.) It’s also possible that he is taking 5 from the 8, and giving it to the first 5 to make 10, and then tacking on the extra 3, to get to 13 (an advanced strategy).

The main point, though, is that you can’t know till you ask him.

And the other point is that it’s often fascinating to open up a dialogue like this with kids, to find out how they do mental math.

Once you get the dialogue underway, I’d suggest that you just follow wherever it leads. For example, if your grandson is using the second strategy I mentioned (making 10 and adding on), ask him if he can extend the process a bit, and do problems like 18 + 5, 28 + 5,
etc.

If, on the other hand, he is “counting up” 5 from the 8, see if he can use the second method, too.

Essentially, what you have here is a great opportunity to find out how your grandson does addition, and to explore the operation with him. And have fun doing it.

Please feel free to write back if you do open up this kind of dialogue. I’d be curious to know what happens.

And to get to the heart of your question, I would say: Yes, you do want your grandson to develop speed or “fluency,” as teachers like to say. But when he is first learning the facts, it’s critical that he think about the operation, not just memorize facts.

To help him gain speed, I would suggest that you use flash cards or fact worksheets (just google math addition worksheets, and you’ll find loads of them).

And to help him develop a range of good strategies to help him learn the facts with understanding,
I suggest the Facts That Last series by Creative Publications.

https://www.creativepublications.com/productfamily.html?PHPSESSID=4c695f197ef3330314c21e50c8b2d70e&familyid=27