3) Data : 15,16,17,23,11,19,20,15,18,22,15,19

4) Mode of the data : The number which is repeated maximum number of time
Data : 15,16,17,23,11,19,20,15,18,22,15,19
From the above data we can see that 15 is repeated maximum number of times
So mode = 15
5) Data : 15,16,17,23,11,19,20,15,18,22,15
For median arrange all the data either from least to greatest or greatest to least
Data from least to greatest : 11, 15,15,15, 16,17,18,19,20,22,23
Number of data = 11
So middle number will be the median
Median = 17
6) Data : 15,16,17,23,11,19,20,15,18,22,15
The first quartile is defined as the middle number between the smallest number and the median of the data set.
Data arranged in lowest to greatest : 11, 15,15,15, 16,17,18,19,20,22,23
For 1st quartile, consider the data as 11, 15,15,15, 16
Middle number = first quartile = 15