Answer:
1st quartile of the data set = 7
Explanation:
Given data set,
1, 5, 7, 9, 11, 16, 18, 20, 30, 35
Median of the given data set is called as "second quartile"
Median of the given set = Average of the terms at the center (Since, the number of data set is even)
=
= 13.5
Number of terms on the left of 13.5 = 5
Term at the center (median) of (1, 5, 7, 9, 11) = 7
Therefore, 1st quartile of the data set = 7