Video Transcript
Multiplying Numbers Using Repeated
Addition
In this video, we will learn how to
multiply numbers up to 100 using repeated addition to help us find the product.
This array shows the number of
stickers a pupil was rewarded with in one week. On Monday, they received two
stickers, another two on Tuesday, two on Wednesday, two on Thursday, and two on
Friday. To find the total number of
stickers they received in a week, we could add together two plus two plus two plus
two plus two. To find the total number of
stickers, we could count in twos: two, four, six, eight, 10. We counted in twos five times —
two, four, six, eight, 10 — because there are five groups of two stickers. So we know that two plus two plus
two plus two plus two equals 10. When we add the same number
together lots of times, we call this repeated addition.
We can also write this as a
multiplication sentence. We counted in twos five times
because there are five groups of two stars. We can also multiply to find the
answer. To write five groups of two as a
multiplication sentence, we would use the multiplication symbol. Two plus two plus two plus two plus
two equals 10, and five times two equals 10.
Let’s practice using repeated
addition to help us multiply. Let’s try some questions.
There are five monsters. Each monster has six eyes. There are five groups of six
eyes. Think about how we can find the
total number of eyes. Anthony says, “I can add what plus
what plus what plus what plus what.” Charlotte says, “I can multiply
what by what.” Help Anthony by writing an addition
expression for the total number of eyes. Help Scarlett by writing a
multiplication expression for the total number of eyes. How many eyes are there?
This question is all about
monsters’ eyes. We’re told there are five monsters
and each monster has six eyes. To find the total number of eyes,
Anthony is going to use repeated addition, and Scarlett is going to multiply to find
the total number of eyes.
Let’s start by helping Anthony to
write his addition expression. If each monster has six eyes,
Anthony will need to add together five lots of six. There are five monsters. Each has six eyes. He needs to add six plus six plus
six plus six plus six. There are one, two, three, four,
five sixes. This is because there are five
monsters and each has six eyes. So, the addition expression which
helps Anthony to find the total number of eyes is six plus six plus six plus six
plus six.
Now we have to help Scarlett write
her multiplication expression. Which two numbers does she need to
multiply? We know there are five monsters and
each monster has six eyes. Five times six is the same as
saying five groups of six. The multiplication expression which
will help Scarlett find out how many eyes there are altogether is five times
six.
Now all we have to do is work out
how many eyes there are altogether. To find six plus six plus six plus
six plus six, or five times six, we need to count in sixes. One six is six, two sixes are 12,
three sixes are 18, four sixes are 24, and five sixes are 30. We added six each time. We’re counting in sixes. The total number of eyes is 30.
The addition expression which
Anthony needs to use to find the total number of eyes is six plus six plus six plus
six plus six. He needs to add together five lots
of six. And the multiplication expression
which Scarlett needs to use to find the total number of eyes is five times six.
There are five monsters and each
monster has six eyes. The total number of eyes is 30.
There are six bunches of
carrots. There are five carrots in each
bunch. How many carrots are there
altogether?
We know that there are six bunches
of carrots. We also know there are five carrots
in each bunch. To find out how many carrots there
are altogether, we could use repeated addition: five plus five plus five plus five
plus five plus five, six lots of five. Six times five is the same as
adding together six lots of five. We could count in fives on a number
line to help. One lot of five or one times five
is five. Two fives are 10, three fives are
15, four fives are 20, five fives are 25, and six fives are 30. Five plus five plus five plus five
plus five plus five, or six times five, is 30. There are 30 carrots
altogether.
Which of the choices is equal to
six times two? Is it six plus six? Two plus two plus two plus two plus
two. Two plus two plus two plus two plus
two plus two plus two. Six. Or six plus six plus six.
In this question, we’ve been given
a multiplication expression, six times two. Six times two is the same as two
groups of six or two lots of six.
We could model two groups of six
using counters. Here’s one group of six, and here’s
another group of six. We know this is not the correct
choice because this just shows one group of six. And six plus six plus six would
mean we would need three groups of six. These two choices can’t be correct
either. These show repeated addition of the
number two. We know there are six in each of
our groups, not two. So this must be the correct
choice. Two groups of six is the same as
saying six plus six. Six plus six is equal to six times
two.
Fill in the blank. Nine plus nine plus nine plus nine
plus nine plus nine is equal to nine multiplied by what.
In this question, we’re shown an
addition expression. We have to add together lots of
nines. And we’re also given part of a
multiplication expression, nine multiplied by what. We have to find the missing number
in the multiplication expression. In other words, nine plus nine plus
nine plus nine plus nine plus nine is equal to nine times what.
To find the missing number, we need
to count how many nines we’re adding together. Let’s count them: one, two, three,
four, five, six. There are six nines. The missing number is six. Nine plus nine plus nine plus nine
plus nine plus nine is equal to nine multiplied by six.
What have we learned in this
video? We’ve learned how to multiply
numbers using repeated addition.
