Find the mean of the data: 12, 15, 18, 20, 25, 30.

Find the median of 12, 7, 15, 9, 20, 11 and 18.

The mean of five numbers is 18. If one number is excluded the mean of the remaining four is 16. Find the excluded number.

The mean of 8 observations is 25. If one observation of 30 is removed, find the mean of the remaining observations.

Find the mean of the first ten natural numbers, and state what happens to the mean if each number is increased by 5.

State one situation in which the median is a better measure of central tendency than the mean, and explain why.

Define the range of a set of observations and find the range of 14, 9, 22, 5 and 18.