Achievement standard

All NZQA documents including past papers and exemplar scripts

Maths is fun - great explanation of standard deviation and variance

Linear Functions of a Random Variable and Sums and Differences of Two independent (usually normal) distributions

These (usually merit/excellence) questions involve using expectation formulas, and sometimes combine these with Normal Distribution questions, or other times are used in Binomial or Poisson distributions for estimating the mean and standard deviation of a Discrete random variable.

Combining Distributions

These are great questions (usually merit or excellence) that involve using one distribution (usually a continuous distribution (normal, triangular or uniform) but could also be Poisson) to get a probability that can then be used to find combined probabilities in a Binomial distribution.