If the data is grouped can you work out the exact mean or do you have to estimate it?

If your data is grouped you most likely have to estimate the mean by assuming the average of the data points within a given interval is the centre of the interval.

An example would be if I was told 5 people had between 25 and 30 tickets to football games within a given season and I was asked to estimate the mean. Here, I must assume the mean of the 5 people’s responses lies directly in the middle of 25 and 30, namely 27.5.