1/2 - математика
1/4 - природоведение
1/7 - разд.
3 - девочки
1/2+1/7+1/4+3=3/4+1/7+3=25/28+3=28 учеников.
102
90*2=180=9=189
100=190=101=191=102=192
3z-2z+15=32
3z-2z=32-15
1z=17
z=17
6t+5t-33=0
6t+5t=33
11t=33
t=3
X/y=7/2⇒x=7/2*y
y/z=6/1⇒z=1/6*y
x+y+z=84
7/2*y+y+1/6*y=84
21y+6y+y=84*6
28y=84*6
y=84*6/28
y=18
x=7/2*18
x=63
z=18*1/6
z=3