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## 'Sort Them Out (1)' printed from http://nrich.maths.org/

This problem provided a good opportunity
to work with each other as a team. The cards gave you some practice
with addition and subtraction, as well as challenging you to
consider different ways of arranging them.

Courtenay and Emily from Ickford Combined
School explained their method of sorting the cards:

We sorted the answers out in the two times table and the four times
table and the ones that are in both times table and another group
which is not in either the two and four times table.

Remember that all numbers in the
four times table will feature in the two
times table.

Caroline from Estes Hills Elementary, North
Carolina, USA (Hello to the USA!) submitted her answer:

At first I sorted ten by itself and the teens together and the
twentys together. Then I noticed that I could sort them by number
order from $10$ to $24$.

Matthew from Stambridge looked at odd
and even numbers:

First we separated the cards into additions and subtractions.

Next we looked at the answers.

In the addition pile we saw that:

E+E=E

O+O=E

E+O=O

O+E=O

In the subtraction pile we saw that:

E-O=O

O-E=O

O-O=E

E-E=E

So, you get an even answer from:

E-E

E+E

O+O

O-O

And so you get an odd answer from:

E-O

E+O

O-E

O+E

Can you think of other ways of arranging
the cards?

Now have a go at Sort Them
Out (2).