Question

A class consists of both boys and girls along with a teacher. After a class, the teacher drinks 9 litres of water, a boy drinks 7 litres of water and a girl drinks 4 litres of water. If after a class 42 litres of water was consumed, find the number of girls in the class ?
A) 8
B) 6
C) 5
D) 3

Answer 1

$\bold{QUESTION-}$A class consists of both boys and girls along with a teacher. After a class, the teacher drinks 9 litres of water, a boy drinks 7 litres of water and a girl drinks 4 litres of water. If after a class 42 litres of water was consumed, find the number of girls in the class ?
A) 8
B) 6
C) 5
D) 3

$\huge\bold{Solution}$

➡️Given - teacher drinks 9 ltr

➡️Let number of boys be 'A'.
➡️Let number of girls be 'B'.

Boy drinks 7 ltr and girl drinks 4 ltr

After class total water consumed = 42 ltr

Then,

9 + 7A + 4B = 42=> 7A + 4B = 33......(By trial and error method,)

➡️The only integers which satisfy the equation is A = 3 and B = 3.

➡️Therefore, number of $\bold{girls}$ in the class = 3.

Hence $\bold{Option -D}$ is Correct

Answer 2

Answer : Option - D, 3

Step-by-step explanation :

Given,
Water consumed by a teacher = 9 litres.

Water consumed by a boy = 7 litres.

Water consumed by a girl = 4 litres.

According to the question, After a class, 42 litres of water was consumed.

Let the number of boys be x,
And the number of girls be y.

So,

9 + 7x + 4y = 42

7x + 4y = 33

Let girls be 3,

7x + 12 = 33
7x = 21
x = 3.
Let girls be 5,
7x + 20 = 33
7x = 13
x = 13/7
Let girls be 6,

7x + 24 = 33.
7x = 9
x = 9/7

Let the girls be 8,
7x + 4(8) = 33
7x = 33 - 32.
7x = 1
x = 1/7

As y = 3 only gives a integral value of x.

Therefore, The number of girls in the class = 3.