If the objects in a group can all be put into pairs without having one left over, then the group has an **even** number of objects.

If the objects in a group are put into pairs and one is left over,

then the group has an **odd** number of objects.

One way to find if the number of slices of pizza is even or odd is to put the slices of pizza into pairs.

An even number equals the sum of two equal numbers.

Put the tickets into two equal groups.

There are 4 tickets in each group.

So, the number that goes in both blanks is 4.