Question

Tìm x:

a) [ 25 - ( x + 1,85 ) ] : 3 = 7

b) 420 : [ 75 - ( x - 10 ) ] = 21

Answer 1

a) [ 25 - ( x + 1,85 ) ] : 3 = 7

[ 25 - ( x + 1,85) ] = 7x3

[ 25 - ( x + 1,85 ) ] = 21

x + 1,85= 25-21

x + 1,85= 4

x= 4-1,85

x= 2,15

Answer 2

a) [25 - (x + 1,85)] : 3 = 7

=> 25 - (x + 1,85)       = 3 x 7

=> 25 - (x + 1,85)       = 21

=> x + 1,85                 = 25 - 21

=> x + 1,85                  = 4

=> x                             = 4 - 1,85

=> x                             = 2,15

b) 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

Answer 3

b) 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

Answer 4

a) [ 25 - ( x + 1, 85 ) ] : 3 = 7

25 - ( x + 1,85 ) = 7 . 3 

25 - ( x + 1,85 ) = 21

x + 1,85 = 25 - 21

x + 1,85 = 4

x = 4 - 1,85

x = 2,15

Vậy x = 2,15

b) 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

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