Answer
21.6
Work Step by Step
$P_{17}$ is the value where 17 % of the values are smaller than $P_{17}$. 17% of the data here is: $40\cdot0.17=6.8$, therefore $P_{17}$ is the 6th value plus the the difference of the 7th and 6th value 0.8 times: $P_{17}=20+(22-20)\cdot 0.8=6+1.6=21.6.$
