The average salary of all the staff in an office of a corporate house is $Rs.\, 5,000$. The average salary of the officers is $Rs.\,14,000$ and that of the rest is $Rs.\,4,000.$ If the total number of staff is $500,$ the number of officers ?
$10$
$15$
$25$
$50$
Find average of all prime numbers between $60$ and $90.$
The average of six numbers is $20 .$ If one number is removed, the average becomes $15 .$ What is the number removed ?
Mr. Patel walked $6\,km$ to reach the station from his house, then he boarded a train whose average speed was $60 \,km / hr$ and thus he reached his destination. In this way he took total of $3\, hours.$ If the average speed of the entire journey was $32\, km / hr$ then the average speed of walking is (in $km/hr$)
There are $35$ students in a hostel. If the number of students increased by $7,$ the expenses of the mess were increased by $Rs.\,42$ per $day$ while the average expenditure per head decreased by $Rs.\,1$, Find out the actual expenditure of the mess. (in $Rs.$ )
A car owner buys petrol at $Rs.\,7.50, Rs.\, 8$ and $Rs.\, 8.50$ per $litre$ for three successive years. What approximately is the average cost per litre of petrol if he spends $Rs.\, 4000$ each year ?(in $Rs.$ )