Find the average of first $25$ multiples of $5 .$
$65$
$60$
$75$
$80$
Sum of first $25$ multiples of $5=5(1+2+3 \ldots .25)$
$=5 \times \frac{25 \times 26}{2}=1625 \Rightarrow$ Average $=\frac{1625}{25}=65$
A man travels by a car to his office at $60 \,km / h$ and returns home along the same route at $20 \,km / h .$ Find the average speed of his whole journey. (in $km/h$)
The average of marks obtained by $120$ candidates was $35.$ If the average of marks of passed candidates was $39$ and that of failed candidates was $15,$ the number of candidates who passed the examination is
The average weight of $6$ persons is increased by $5\, kg$ when one of them who weighs $40\, kg$ is replaced by a new man. The weight of new man is (in $kg$)
The average of a collection of $20$ measurements was calculated to be $56\, cm .$ But later, it was found that a mistake had occurred in one of the measurements which was recorded as $64 \,cm ,$ but should have been $61 \,cm$. The correct average must be? (in $cm$)
The mean weight of $150$ students in a class is $60 \,kg.$ The mean weight of boys is $70\, kg$ and that of girls is $55 \,kg$. What is the number of boys in the class?
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