Answer: 90
Explanation:
An outlier of a data set is a data value which is different from all the values in the data set.
The given data set : {40, 35, 44, 90, 23, 25, 28, 35}
Here we can see 90 is the data value which is different from others as it is a much bigger number than others, thus 90 is considered as the outlier.