Question

a) Thực hiện phép tính: 2011 : { 639 : [ 316 – ( 78 + 25 )] : 3 }

b) Tìm số tự nhiên x, biết: ( 3x – 23 ) . 7 = 74

c) Tìm số tự nhiên x, biết: ( 8705 + 5235 ) – 5x = 3885.

Answer 1

a) 2011 : { 639 : [ 316 – ( 78 + 25 )] : 3 }

= 2011 : { 639 : [ 316 – 103 ] : 3}

= 2011 : ( 639 : 213 : 3 ) = 2011 : (3 : 3 ) = 2011 : 1 = 2011

b) ( 3x – 23) . 7 = 74

3x – 8 = 74 : 7

3x – 8 = 73

3x – 8 = 343

3x = 343 + 8

3x = 351

x = 351 : 3 = 117

c) (8705 + 5235) – 5x = 3885

13940 – 5x = 3885

5x = 13940 – 3885

5x = 10055

x = 10055 : 5 = 2011

Answer 2

Trl:

a) \(2011:\left\{639:\left[316-\left(78+25\right)\right]:3\right\}\)

\(=2011:\left\{639:\left[316-103\right]:3\right\}\)

\(=2011:\left\{639:213:3\right\}\)

\(=2011:1\)

\(=2011\)

b) \(\left(3x-23\right).7=74\)

\(\Rightarrow3x-23=74:7\)

\(\Rightarrow3x-23=10,5\)

\(\Rightarrow3x=10,5+23\)

\(\Rightarrow3x=33,5\)

\(\Rightarrow x=33,5:3\)

\(\Rightarrow11,1\)( Câu này sai đề nha )

c) \(\left(8705+5235\right)-5x=3885\)

\(\Rightarrow13940-5x=3885\)

\(\Rightarrow5x=10055\)

\(\Rightarrow x=10055:5\)

\(\Rightarrow x=2011\)