Lower quartile is defined as the mid value of the first half of the data set when the data set is arranged in ascending order. Lower quartile in other words separates the lowest 25% from the highest 75% of the data.
The lower quartile of the data set for the blood glucose levels of 10 individuals is given by the mid value of the first five terms 88, 97, 101, 104 and 104.
Thus the mid value of this first half term is 101. Thus the lower quartile of the data set is 101.