This question was previously asked in

Territorial Army Paper I : Official Practice Test Paper - 2

Option 1 : \(\dfrac{ma-nb}{m-n}\)

**Given**

The average age of m boys in a class is 'a' year. If the average of n of then is 'b' years

**Concept used**

Average = (sum of observations) / Number of observations

**Calculation**

Sum of ages of m boys = a × m

Sum of ages of n boys = b × n

Sum of ages of remaining boys = \(\frac{{ma - nb}}{{m - n}}\)