Question

In a room, there are 450 students of which 20% are girls. A group of students have mobile phones with them, of which 40% are girls. Of those students without a mobile phone, only 10% are girls. How many boys have mobile phones in that room?

Answer 1

Answer:

90

Step-by-step explanation:

Total number of students = 450

20 % are girls

So, number of girls = $20\% \times 450$

                               = $\frac{20}{100} \times 450$

                               = $\frac{1}{5} \times 450$

                               = $90$

Now let no. of students having mobile phones be x

So, number of students not having mobile phones = 450-x

Now we are given that  A group of students have mobile phones with them, of which 40% are girls

So, This implies 60% of boys out of x having mobile phones.

So, number of girls having mobile phone =$\frac{40}{100}x$

Now we are given that Of those students without a mobile phone, only 10% are girls

So, number of girls not having mobile phone =$\frac{10}{100}(450-x)$

So, total number of girls :

= $\frac{40}{100}x+\frac{10}{100}(450-x)=90$

= $4500-10x+40x=9000$

= $4500+30x=9000$

= $30x=4500$

= $x=\frac{4500}{30}$

= $x=150$

So, Number of boys having mobile phone =$\frac{60}{100} \times 150$

                                                                       =$90$

Hence there are 90 boys have mobile phones in that room.

Answer 2

Answer:

216 boys

Step-by-step explanation:

450 students: 20% girls, 80% boys

450*20%=90 girls

450*80%=360 boys

Students having mobile phones: 40% (OF THE 90) girls, 60% (OF THE 360) boys

90*40%=36 girls

360*60%=216 boys

[We honestly don't need to care about the girls without mobile phones as they are only asking how many boys have mobile phones]