a,
72 : ( 3*x ) = 4
x = 72 : 4
x = 18
x = 18 : 3
x = 6 .
b,
400 : ( x*5 ) = 8
x = 400 : 8
x = 50
x = 50 : 5
x = 10 .
ủng hộ ! 
Nobita
\(a,72:\left(3\times x\right)=4\)
\(3\times x=72:4\)
\(3\times x=18\)
\(x=18:3\)
\(x=6\)
\(b,400:\left(x\times5\right)=8\)
\(x\times5=400:8\)
\(x\times5=50\)
\(x=50:5\)
\(x=10\)
a, 72 : ( 3 * x ) = 4
3 * x = 72 : 4
3 * x = 18
x = 18 : 3
x = 6
b, 400 : ( x * 5 ) = 8
x * 5 = 400 : 8
x * 5 = 50
x = 50 : 5
x = 10
a, 72 : (3*x) = 4
( 3 * x )= 72 : 4
( 3 * x) = 18
x = 18 : 3
x = 6
Vậy x = 6
b, 400 :(x*5)= 8
( x * 5 ) = 400 : 8
x * 5 = 50
x= 50 : 5
x = 10
Vậy x = 10
a, 72 : (3 . x) = 4
(3 . x) = 72 : 4
3 . x = 18
x = 18 : 3
x = 6
b, 400 : (x . 5) = 8
x . 5 = 400 : 8
x . 5 = 50
x = 50 : 5
x = 10