Multiplying by Seven
In this video, we’re going to learn
how to model multiplication by seven and recite the seven times table.
Let’s start by practicing our seven
times table. One times seven is seven. Two times seven is 14. Three times seven is 21. Four times seven is 28. Five times seven is 35. Six times seven is 42. Seven times seven is 49. Eight times seven is 56. Nine times seven is 63. 10 times seven is 70. 11 times seven is 77. 12 times seven is 84. When we recite our seven times
table, we’re counting forward in sevens.
Here’s an array which shows one
group of seven. And we know that one times seven
equals seven. We could also say seven times one
equals seven. If we make two groups of seven, we
will have 14 counters because two times seven is 14. And if we add seven more, we’ll
have three groups of seven, which are 21. We could model the seven times
table all the way up to 12 times seven using an array. 12 groups of seven or 12 lots of
seven are 84. 12 times seven is 84.
Let’s recap the strategies we’ve
learned to help us multiply by seven. We could use our knowledge of the
seven times table, we could count in sevens on a number line, and we could use a
model like this array. Let’s practice using some of these
strategies to help us answer some questions.
Calculate seven times four.
To find seven times four or four
times seven, we could use our knowledge of the seven times table. This array shows one group of
seven. One lot of seven is seven. If we add another group of seven,
we have 14. Double seven is 14. In this question, we’re multiplying
seven by four. And we know that four is double
two. So, if two times seven is 14, we
can double this fact to find four times seven. Four times seven is double 14,
which is 28. Seven times four or four times
seven is 28. We used our knowledge of the seven
times table and doubling to calculate the answer.
Notice how each row is seven more
than the previous one. One times seven equals seven, two
times seven equals 14, three times seven equals 21. Find the result of the following:
five times seven equals what. Find the result of the following:
seven times seven equals what.
This question is all about the
seven times table. The first model shows one lot of
seven. Then, we add seven more to show two
lots of seven and seven more to show three lots of seven. As we add seven each time, the
result increases by seven. One times seven is seven, two times
seven equals 14, and three times seven equals 21. As we add seven, we’re counting on
in sevens. One seven is seven; two sevens are
14; three sevens are 21.
We’re being asked to find the
result of five times seven. So, if three times seven is 21, we
just need to add seven more to find four times seven. 21 plus seven is 28. And we can add one more seven to
find five times seven. What is 28 plus seven? It’s 35. Finally, we have to find the result
of seven times seven. We already know that five times
seven is 35. To find six times seven, we just
need to add another seven. 35 plus seven is 42. And to find seven times seven, we
just need to add one more seven.
We knew from the model that one
times seven is seven, two times seven is 14, and three times seven is 21. We continued counting forward by
seven each time to find five times seven, which is 35, and seven times seven, which
is 49. When we’re multiplying by seven, we
can skip count by seven to help us find the result.
Find seven multiplied by three. Hint: How can knowing five times
three help you?
In this question, we have to find
seven multiplied by three. And we’ve been given this model to
help us. And we’re also given a hint that
tells us to think about how knowing five times three can help us to find seven times
three. This model shows three lots of
seven cubes. Did you notice how the seven has
been broken apart into five cubes and two cubes? We know that we can partition the
number seven into five and two because five and two make seven. So, we can find seven times three
by first multiplying five by three and then multiplying two by three.
What is five times three? Five times three is 15. Now, we can calculate two times
three, which is six. And if we add 15 and six together,
we get 21. We found seven times three by
partitioning or breaking the number seven apart into five and two. First, we found five times
three. Then, we found two times three. We multiplied each part by
three. And we can add the parts back
together again to find the product of seven times three. If five times three is 15 and two
times three is six, then seven times three is 21.
What have we learned in this
video? We have learned how to multiply by
seven using our knowledge of the seven times table, skip counting in sevens or
counting forward in jumps of seven, and using models like this array.