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G'day students, I'm Dr Price, I'm going to teach you today about how to remember the
"5x Tables". So I've started off writing the 5x tables here and I've expect you've already
looked at them and so you'll know how this pattern goes. We start with "5, 10, 15 then
we have 20, 25, 30, 35, 40, 45". "You can see a pattern can't you?" The number ones
is going "5, 0, 5, 0, 5, 0" all the way, we can continue this, "50, 55, 60" and so it
will go on and on if we keep on adding 5. So what I want you to think about is, "Why
does it keep going 5 and then 0 and 5 and then 0?" We'll if you look at your hands you
might get a clue, if you look at the digits, the thumb in the fingers in one hand of course
there are 5 of them. If you have a second hand and put it next to it, of course that
makes "10". So every time we have 2 fives that makes "10", and so we have this round
numbers "10, 20, 30, 40, 50" and so on, every second answer in the 5x table is one of those
round numbers and the next number after that has a 5 in the end. So after 30 we have 35
and then 40 and then the next one is 45 and so on. Here's some 10 frames, and I've started
putting some counters out and this will show us the same thing in another way, so here
we have "5 and 5 and of course, 5 and 5 makes 10, Pairs of 5 makes 10". "What if we had
another 5?" Of course that will make 10 and 5. Let me write some more numbers down, "10
+ 5" and of course that's "15", and so that is going to be our pattern all the way through
the 5x table. Let's look at another way of thinking about this; I'm going to push this
together into long columns. So, that's not very straight is it? There we go, here we
have columns of 10 and of course there are 3 columns. "How many are 3 tens?" Of course
3 tens make 30. "What if I removed half of them down here?" Now we have 5 in a column
and there are still 3 columns. "What are 3 fives?" So this is one of our times tables
or number facts. 3 fives must be half of the 30 that we started with and of course half
of 30 is "15". So another way of thinking about the 5x tables is to think, "What is
half the number of tens?" So let me show you what I mean. Supposing we had 6 x 5, and we
say "What is 6 x 5?" "What would 6 x 10 be equal to?" 6 x 10 of course is "60", because
that's what we call 6 tens. Half of 6 x 10 will be 6 x 5, "What is half of 60?" That's
30. So if we just do that every time we can get the right answer. It helps if this is
an even number because half an even number is a whole number. "What about a harder one?"
Supposing the question was 9 x 5? "How would you work out the answer?" Well we could do
the same thing. "What is 9 x 10?" 9 tens are "90", "What's half of 90?" That is harder
you have to think of it more carefully. Half of 9 will be 4 and a half, because 2 fours
are 8. So 4 and a half will be 4 tens a 40, half 10 is 5, its "45". There are a number
of ways to think about it but it's always going to come back to "2 fives make 10". So
hope this has been helpful, and I will talk to you next time.