Same mean, different spread

Two classes both have a mean mark of 60. You will write the standard deviation and the range, and let the program say which class is steadier. Then it draws both classes on one number line.

The idea. The standard deviation is the square root of the mean of the squared distances from the mean. A smaller one means the marks stay closer together.

Your tasks.

1. In sd, return the standard deviation of values.
2. In rng, return the largest value minus the smallest.
3. Set steadier to the name of the class with the smaller standard deviation.