420:[75-(x-10)]=21
=> 75 - ( x-10) = 420 : 21 = 20
=> x -10 = 75 -20 = 55
=> x = 55 + 10 = 65
420 : [75 - (x - 10)] = 21
75 - (x - 10) = 420 : 21
75 - (x - 10) = 20
x - 10 = 75 - 20
x - 10 = 55
x = 55 + 10
x = 65
Vậy x = 65
\(420:\left[75-\left(x-10\right)\right]=21\)
\(75-\left(x-10\right)=420:21\)
\(75-\left(x-10\right)=20\)
\(x-10=75-20\)
\(x-10=55\)
\(x=55+10\)
\(x=65\)
420:[75-(x-10)]=21
=> 75 - ( x-10) = 420 : 21 = 20
=> x -10 = 75 -20 = 55
=> x = 55 + 10 = 65
420 :[75 - (x - 10) = 21
75- (x- 10) = 420 : 21
75- (x- 10) = 20
x- 10 = 75 - 20
x - 10 = 55
x = 55 +10
x = 65
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