Mean weight of 150 students in a class is 60 ,kg. mean weight of boys is 70, kg and that of girls is

English

Gujarati

Hindi

4.Average

medium

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?

A

$50$

B

$60$

C

$75$

D

$100$

Solution

Let the no of boys in a class $=x$

$\therefore x \times 70+(150-x) 55=150 \times 60$

$70 x-55 x=9000-8250 \Rightarrow 15 x=750$

$x=50 \Rightarrow$ No. of boys $=50$

Standard 13

Quantitative Aptitude

Share

Similar Questions

The average salary of $15$ persons is $Rs.\, 5,500.$ If the salary of one person is added, the average increase to $Rs. \,5,700 .$ What is the salary of this one person in $Rs. \, ?$

medium

The average marks obtained by $40$ students of a class is $86 .$ If the $5$ highest marks are removed, the average reduces by one mark. The average marks of the top $5$ students is

hard

There were $35$ students in a hostel. If the number of students increases by $7,$ the expenses of the mess increase by $Rs. \,42$ per $day$ while the average expenditure per head decreases by $Rs.\, 1 .$ Find the original expenditure of the mess in $Rs.$

medium

The average marks of a group of $20$ students on a test is reduced by $4$ when the topper who scored $90$ marks is replaced of a new students. Find the marks of the new student.

easy

The average weight of a group of $20$ boys was calculated to be $89.4 kg$ and it was later discovered that one weight was misread as $78 kg$ instead of the correct one of $87 kg$. The correct average weight is in $kg$

medium