A Problem of Time

Consider a watch face which has identical hands and identical marks for the hours. It is opposite to a mirror. When is the time as read direct and in the mirror exactly the same between 6 and 7?

Eight Dominoes

Using the 8 dominoes make a square where each of the columns and rows adds up to 8

Holly

The ten arcs forming the edges of the "holly leaf" are all arcs of circles of radius 1 cm. Find the length of the perimeter of the holly leaf and the area of its surface.

A Roll of Patterned Paper

Stage: 4 Challenge Level:

In what follows I'm going to call the design above the "unit shape" and imagine it repeated endlessly along a line - rather like a stream of paper coming off a roll.

Here are two pieces from the roll :

The second piece has then been turned around (rotated 180 $^\circ$).

Try to design a new unit shape (probably simpler than mine) to make a strip which looks the same after a 180 $^\circ$ rotation.

In other words, make it so that you could not say whether the torn off strip had or had not been rotated.

There are two possibilities: across and along

First the original strip could have a mirror across it.

This illustration shows the right side as the reflection of the left side

Can you create a unit shape so that the strip has reflection symmetry across a vertical mirror line ?

And where would the mirror line need to be to be placed ?

Now try a mirror 'along' the torn off strip

The mirror could be reflecting the top half,

or (below) the bottom half.

Can you make a strip that has reflection symmetry across a horizontal mirror line ?

If you'd like more of this sort of thing, try the problem called 'One Reflection Implies Another'.