Question

Some of the students were asked how much time they spent revising for the test. $10$ students revised for $2.5$ hours, $12$ students revised for $3$ hours and $n$ students revised for $4$ hours.
The mean time that these students spent revising was $3.1$ hours.
Find $n$

Answer 1

total student $=10+12+n=(22+n)$student

$\therefore$ total time $=10x2.5+12x3+nx4=25+36+4n$

$\therefore$ total time $=61+4n$

$\therefore$mean time=$\frac{totaltime}{totalstudent}$

$\therefore 3.1=\frac{61+4n}{22+n}$

$\therefore \left(3.1\right)(22+n)=61+4n$

$\therefore 68.2+3.1n=61+4n$

$\therefore 0.9n=7.2$

$\therefore n=7.2=8$

$\therefore$ value of n is $8$.