5 A survey of the time people spent travelling to work one morning gave these results. a How many people were involved in the survey? b Write down the modal class. c Estimate the median journey time. d Estimate the mean journey time. Journey time Up to 30 minutes 30 minutes or more but less than one hour One hour of more but less than 1 hours 1 hours or more but less than two hours Frequency 15 30 10 2​