Mathematica Tutorial 2 - Introduction to Lists. Part 2: Table and Visualizing Lists

Tutorial 2 for Math 250 at Queens College.

[emmanuelschmulewitz]

Good video, thanks!
For some reason I'm interested in the following:
-taking population age data from 3 groups, for simplicity e.g. created by using RandomReal[] and 10000 values per list
-adding it up and display that subset of all 3 lists with the values adding up to 20 or larger
--> How old are all the people within their respective group, whose sum is older than 20?
Is there a way to implement it in Mathematica and to output the three lists of groups a={}, b={}, c={} => \[CapitalSigma] >20 ?
That would be nice, by now I struggle with applying the condition on the list and extract all elements fulfilling this condition.