Question:Find the average of first 30 natural numbers.
Sum of first 30 natural numbers =`((30 xx 31)/2)` = 465 `:.` Required average = `465/30` = 15.5
Question:Find the average of first 25 multiples of 3.
Required average = `(3(1 + 2 + 3 + ..... +25))/25` =`((3 xx 25 xx 26)/(2 xx 25))` =39
Question:The average age of a class of `39` students is `15` years. If the age of the teacher be included, then the average increases by 3 months. Find the age of the teacher.
Total age of 39 persons `= (39 x 15)` years `= 585` years. Average age of 40 person `= 15` years `3` months `= 61/4` years. Total age of the 40 person `= (61/4) xx 4` years `= 610` years. `:.`Total age of 40 person `= (610 - 585)` Years `= 25` years.
Question:The average age of a class of 39 students is 15 years. If the age of the teacher be included, then the average increases by 3 months. Find the age of the teacher?
The total age of 39 persons =(39 x 15) years = 585 years. Average age of 40 person =15 years 3 months =`(61/4)` years. Total age of 40 person = `(61/4 xx 40)` years =610 years. `:.` Age of the teacher= (610 x 585) years = 25 years.
Question:The average weight of `10` oarsmen in a boat is increased by `1.8 kg` when one of the crew, who weights `53` kg is replaced by a new man. Find the weight of the crew, who weights `53 kg` is replaced by a new man. Find the weight of the new man.
Total weight increased `= (1.8 xx 10)` kg `=18` kg. `:.` Weight of the new man `= (53 + 18 )` kg `=71` kg