The average age of $8$ members of a group is $40 \,years.$ The age of $1$ member is $55\, years.$ After his retirement a new member comes in his place of age $39 .$ What is the effect of his retirement on the average age of group ?
$2$
$0$
$3$
$5$
A man covers $\frac{1}{3}$ of his journey by train at $80\, km / h ,$ next $\frac{1}{3}$ by $60\, km / h$ and the rest by bicycle at $30 \,km / h$. Find the average speed of the man during the whole journey. (in $km/h$)
The average age of a group of persons going for a picnic is $16.75 \,years.$ $20$ new persons with an average age of $13.25 \,years$ join the group on the spot due to which the average of the group becomes $15\, years.$ Find the number of persons initially going for the picnic $?$
The average of five consecutive even numbers starting with $4,$ is
In a class, average height of all students is '$a$ ' cms. Among them, average height of $10$ students is '$b$' cms and the average height of the remaining students is '$c$' cms. Find the number of students in the class. (Here $a>c$ and $b>c$ )
The cost of $5 \,kg$ of apples is $Rs.\, 450 .$ The cost of $12$ dozen mangoes is $Rs.\, 4320$, and the cost of $4 \,kg$ of oranges is $Rs.\,240.$ What is the total cost of $8 \,kg$ of apples$, 8$ dozens of mangoes and $8 \,kg$ of oranges ? (in $Rs.$)