2.
Mrs Hippo has lost all the little hippos from
her class. She is very forgetful teacher.
She doesn’t remember how many little hippos
belong in her class.
Before we start looking, can we help Mrs
Hippo work out how many little hippos are in
her class?
3.
Mrs Hippo thinks and thinks and then she
remembers!
There were 8 groups of little hippos.
There were 3 little hippos in each group.
Um…. How many is that altogether?
We could add all the groups together, but
because we know that each group of little
hippos is the same we can work it out another
way.
4.
Let’s look at the first group of little hippos.
How many hippos can you see?
We can see three little hippos standing
together.
5.
Look! More little hippos have joined the first
group.
How many little hippos are in this group?
There are three more little hippos.
Put your thinking caps on to work out how many
little hippos altogether. How could we easily
work it out?
We have two groups of three hippos in each
group.
We can double the number in each group, so
double 3 is 6.
This means 3 by 2 is 6. We have found six hippos.
6.
More little hippos have joined their friends.
How many more little hippos can you see?
There are two more groups of three, so there
are six more little hippos.
Put your thinking caps on to work out how
many little hippos altogether.
Now we have four groups, with three hippos in
each group. We can double and then double
again. If double 3 is 6, 3 multiplied by 4 means
double 6, which equals 12.
So 3 by 4 is 12. We have found 12 hippos now.
7.
We can see lots more little hippos.
How could we easily work it out how many
now?
Remember we don’t need to count each one!
Count the number of groups.
Now we have eight groups, with three hippos
in each group.
8.
To work out how many little hippos altogether
we can use the doubling strategy.
We can double, double and then double again.
We start with our first group of three little
hippos.
11.
Finally we double, double, double.
So double 12 is 24.
Altogether we can see 24 little hippos.
8 groups of 3 makes 24.
Mrs Hippo needs to find 24 little hippos.
This story about doubling showed us a special
strategy where we can double, double, double
when there are eight groups of equal numbers.
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