Tips & Tricks Given: Average of 15 observations = 23. Concept: When the same changes take place in each observation of a group, then the same change takes place for the average of those observations. Calculation: Thus, instead of adding 7 to each term, we only do the changes to the average of these terms to get the required new average. ∴ Required new average = 7 + old average= 7 + 23 = 30 = 30