If each observation in a data is decreased by two, their :

1. mean decreases by 2, but median remains same.

2. mean remains same, but median decreases, by 2.

3. mean and median both decrease by 2.

4. mean and median both remain the same.

As we know, the median is the value of the middle term for any given set of data.

If each observation in a data is decreased by 2, both the mean and median will also decrease by 2.

Hence, option 3 is the correct option.