Out of four numbers the average of the first three is $16$ and that of the last three is $15 .$ If the last number is $20$ then the first number is
$21$
$23$
$28$
$25$
The average income of $A$ for $15$ days is $Rs.\,70.$ The average for first five days is $Rs.\, 60$ and that for the last nine days is $Rs.\,80.$ A's income for the sixth day is (in $Rs.\,$ )
If the average marks of three batches of $55,60$ and $45$ students respectively is $50,55$ and $60 ,$ then the average marks of all the students is
The mean of $11$ numbers is $35 .$ If the mean of first $6$ numbers is $32$ and that of the last $6$ numbers is $37,$ then find the sixth number.
The average age of $15$ students of a class is $15\, year.$ Oute of these, the average age of $5$ students is $14 \,year$ and that of the other $9$ students is $16\, year.$ The age of the $15^{th}$ students is? (in $year$)
In a school, the average age of students is $6 \,years$ , and the average age of $12$ teachers is $40\, years.$ If the average age of the combined group of all the teachers and students is $7 \,years$ , then the number of students is?