The median-calculating recursive call does not exceed worst-case linear behavior because the list of medians is 20% of the size of the list, while the other recursive call recurses on at most 70% of the list.
* the ''T(n·7/10)'' part is for the actual Quickselect recursion (for the worst case, in which the ''k''-th element is in the bigger partition that can be of size n·7/10 maximally) .