### Which Twin Is Older?

A simplified account of special relativity and the twins paradox.

### Snookered

In a snooker game the brown ball was on the lip of the pocket but it could not be hit directly as the black ball was in the way. How could it be potted by playing the white ball off a cushion?

### Spokes

Draw three equal line segments in a unit circle to divide the circle into four parts of equal area.

# Scale Invariance

##### Age 16 to 18 Challenge Level:

Don't forget that probability distribution functions must integrate to $1$ over the allowed range of values.

Try changing variables for the first part.

For the second part, note that clearly $x^2\rightarrow (ax)^2 \neq a(x^2).$

How could you make the two sides match for other powers of $x$?