it's 8,
let the no. of tired students be x
add all the numbers of the happy, hungry and in between students and then subtract from the total of the student
which has to look smth like this
happy = 10
so we fill all the numbers in between then we add them and see what's missing
1+3+2 = 6
10-6 = 4
4 students are happy
hungry = 7
1+1+3 = 5
7-5 = 2
2 students are hungry
and lastly for tired, they didn't mention the total so we add all the numbers we got and subtract them by the total of students (just like mentioned above)
2+1+1+3+4+2 = 13
21-13 = 8
8 students were tired
x = 8
