Source: TheAnimatedClassroom
http://www.bbc.co.uk/schools/gcsebitesize/maths/statistics/measuresofaveragerev_print.shtml
http://www.bbc.co.uk/schools/gcsebitesize/maths/activities/mean/mean.shtml
Source: GCSE BBC Bitesize
https://www.khanacademy.org/math/cc-seventh-grade-math/cc-7th-probability-statistics/cc-7th-central-tendency/e/mean_median_and_mode
Source: Khan Academy
Source: Yourteachermathhelp