The average of $13$ results is $50$. If the average of the first $7$ results is $52$ and that of the last $7$ results is $49$,find the $7^{th}$ result.

$A$ person covers $9 \, km$ with a speed of $3 \, km/h$,$25 \, km$ with a speed of $5 \, km/h$,and $30 \, km$ with a speed of $10 \, km/h$. Find the average speed of the person in $km/h$.

The average of the squares of the first ten natural numbers is

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,$8$ dozen mangoes,and $8 \,kg$ of oranges? (in $Rs.$)

The average age of a family of $6$ members $4$ years ago was $25$ years. Meanwhile,a child was born in this family,and the average age of the whole family is still the same today. The present age of the child in years is?

Visitors to a show were charged $Rs. 15$ each on the first day,$Rs. 7.50$ on the second day,$Rs. 2.50$ on the third day,and the total attendance on the three days was in the ratio $2:5:13$ respectively. The average charge per person for the entire three days is (in $Rs.$):