The data needs to be converted to continuous classes for finding the median, since the formula assumes continuous classes. The classes then change to (117.5−126.5,126.5−135.5,...,171.5−180.5.)Converting the given table into exclusive form and preparing the cumulative frequency table, we getWe have, n=40⇒2n​=20The cumulative frequency just greater than 2n​ is 29 and the corresponding class is 144.5−153.5.Thus, 144.5−153.5 is the median class such that2n​=20,l=144.5,cf=17,f=12, and h=9Substituting these values in the formulaMedian, M=l+⎝⎛​f2n​−cf​⎠⎞​×hM=144.5+(1220−17​)×9M=144.5+123​×3=144.5+2.25=146.75       Hence, median length =146.75 hours