Statistics & probability

These three “averages” each summarise a data set. The mean adds all the values and divides by how many there are: for 2, 4, 6, 8 the mean is 20 ÷ 4 = 5. The median is the middle value once the data is sorted (average the two middles if there is an even count). The mode is the value that appears most often.

The range measures how spread out the data is: subtract the smallest value from the largest. For 4, 9, 2, 7 the range is 9 − 2 = 7. A small range means the values are bunched together; a large range means they are spread out.

When every outcome is equally likely, the probability of an event is the number of favourable outcomes divided by the total number of outcomes. Rolling an even number on a fair die has 3 favourable faces (2, 4, 6) out of 6, so the probability is 3 ÷ 6 = 0.5. Probabilities always sit between 0 (impossible) and 1 (certain).