So, for medians, consider the following approach: Consider data collected into disjoint intervals of the form
\(\displaystyle [a_1,b_1)\)
\(\displaystyle [a_2,b_2)\)
\(\displaystyle [a_3,b_3)\)
...
\(\displaystyle [a_n,b_n)\)
where \(f_k\) is the frequency of data items in interval \([a_k,b_k)\) with corresponding cummulative frequency \(F_k\text{.}\) Again, order them from low to high so that \(b_1 \le a_2, b_2 \le a_3\text{,}\) etc.