g) 42 - (x + 1).3=38 : 36
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1 . (15+37)+(52-37-17)
= 15+37+52-37-17
=(15-17)+(37-37)+52
= -2+0+52 = 50
2. (27+65)+(346-27-65)
= 27+65+346-27-65
=(27-27)+(65-65)+346
=0+0+346
=346

36 + 48 + 40 + 42 + 44 + 46 + 48 + 50
= (36 + 48) + (40 + 50) + (42 + 48) + (44 +46)
= 84 + 90 + 90 + 90
= 74 + 90 \(\times\) 3
= 74 + 270
= 344
36 + 38 + 40 + 42 + 44 + 46 + 48 + 50
= (36 + 50){ (50-36):2+1}: 2
= 344



a) 36 x (7 + 3) = ?
Cách 1: 36 x (7 + 3)
= 36 x 10 = 360
Cách 2: 36 x (7 + 3)
= 36 x 7 + 36 x 3 = 360
+) 207 x (2 +6) =?
Cách 1: 207 x (2 +6)
= 207 x 8 = 1656
Cách 2: 207 x (2 +6)
= 207 x 2 + 207 x 6 = 1656
b) 5 x 38 + 5 x 62 =?
Cách 1: 5 x 38 + 5 x 62
= 190 + 310 = 500
Cách 2: 5 x 38 + 5 x 62
= 5 x (38 +62) = 5 x 100 = 500
+) 135 x 8 + 135 x 2 =?
Cách 1: 135 x 8 + 135 x 2
= 1080 + 270 = 1350
Cách 2: 135 x 8 + 135 x 2
= 135 x (8 + 2) = 1350
Nói thêm: Nếu tính theo cách 1 thì nhanh hơn.
Tính và so sánh giá tri của biểu thức:
(3 +5) x 4 và 3 x 4 + 4 x 5
Từ kết quả so sánh, nêu cách nhân một tổng với một số.

a, [ 58+(-42)]-(58-42)
= 58 - 42 - 58 + 42
= ( 58 - 58 ) + ( 42 - 42)
= 0+0=0
b, ( 65 - 35 ) - ( 35 + 27 )
= 65 - 35 - 35 - 27
= 65 - 70 -27
= 65 - 97
= -32
c, 3 . 52 - 176 : 23
=3 .25 - 176 : 8
= 75 - 22
= 53
d, 22 . 3 - 5 . 23
= 4 . 3 - 5 . 8
= 12 - 40
= -28
g, 2020 - [ 39 - ( 5 - 1 )2 ] - 2019
= 2020 - [ 39 - 42 ] - 2019
= ( 2020 -2019 ) - [ 39 - 16 ]
= 1 - 23
= -22
k, 2018 : [ 38 - ( 7 - 1 )2 ] + 20180
= 2018 : [ 38 - 62 ] + 1
= 2018 : [ 38 - 36 ] + 1
= 2018 : 2 + 1
= 1009 + 1 =1010
a)\(\left[58+\left(-42\right)\right]-\left(58-42\right)\)
=\(58-42-58+42\)
=\(0\)
b)\(\left(65-35\right)-\left(35+27\right)\)
=\(65-35-35+27\)
=\(-32\)
c)\(3.5^2-176:2^3\)
=\(75-22\)
=\(53\)
d)\(2^2.3-5.2^3\)
=\(2^2\left(3-10\right)\)
=\(-28\)
g)\(2020-\left[39-\left(5-1\right)^2\right]-2019\)
=\(1-\left(39-16\right)\)
=\(-22\)
k)\(2018:\left[38-\left(7-1\right)^2\right]+2018^0\)
=\(2018:2+2018^0\)
=\(1010\)


Bài 2:
a: \(\dfrac{1}{4};\dfrac{2}{5}\)
\(\dfrac{1}{4}=\dfrac{1\cdot5}{4\cdot5}=\dfrac{5}{20}\)
\(\dfrac{2}{5}=\dfrac{2\cdot4}{5\cdot4}=\dfrac{8}{20}\)
\(\dfrac{2}{3};\dfrac{7}{8}\)
\(\dfrac{2}{3}=\dfrac{2\cdot8}{3\cdot8}=\dfrac{16}{24}\)
\(\dfrac{7}{8}=\dfrac{7\cdot3}{8\cdot3}=\dfrac{21}{24}\)
\(\dfrac{3}{4};\dfrac{5}{6}\)
\(\dfrac{3}{4}=\dfrac{3\cdot3}{4\cdot3}=\dfrac{9}{12}\)
\(\dfrac{5}{6}=\dfrac{5\cdot2}{6\cdot2}=\dfrac{10}{12}\)
b: \(\dfrac{1}{3};\dfrac{7}{9}\)
\(\dfrac{1}{3}=\dfrac{1\cdot3}{3\cdot3}=\dfrac{3}{9}\)
\(\dfrac{7}{9}=\dfrac{7\cdot1}{9\cdot1}=\dfrac{7}{9}\)
\(\dfrac{3}{4};\dfrac{9}{24}\)
\(\dfrac{3}{4}=\dfrac{3\cdot6}{4\cdot6}=\dfrac{18}{24}\)
\(\dfrac{9}{24}=\dfrac{9\cdot1}{24\cdot1}=\dfrac{9}{24}\)
\(\dfrac{7}{10};\dfrac{19}{30}\)
\(\dfrac{7}{10}=\dfrac{7\cdot3}{10\cdot3}=\dfrac{21}{30}\)
\(\dfrac{19}{30}=\dfrac{19\cdot1}{30\cdot1}=\dfrac{19}{30}\)
Bài 1:
\(\dfrac{36}{108}=\dfrac{36:36}{108:36}=\dfrac{1}{3}\)
\(\dfrac{28}{30}=\dfrac{28:2}{30:2}=\dfrac{14}{15}\)
\(\dfrac{42}{98}=\dfrac{42:14}{98:14}=\dfrac{3}{7}\)
\(\dfrac{15}{120}=\dfrac{15:15}{120:15}=\dfrac{1}{8}\)
\(\dfrac{84}{364}=\dfrac{84:28}{364:28}=\dfrac{3}{13}\)
\(\dfrac{120}{100}=\dfrac{120:20}{100:20}=\dfrac{6}{5}\)
\(\dfrac{418}{38}=\dfrac{418:38}{38:38}=\dfrac{11}{1}=11\)
\(\dfrac{96}{1056}=\dfrac{96:96}{1056:96}=\dfrac{1}{11}\)
\(\dfrac{3838}{4040}=\dfrac{3838:101}{4040:101}=\dfrac{38}{40}=\dfrac{38:2}{40:2}=\dfrac{19}{20}\)
\(\dfrac{119119}{123123}=\dfrac{119119:1001}{123123:1001}=\dfrac{119}{123}\)
42 - (x + 1).3=38 : 36
42 - (x + 1).3=38-6
42 - (x + 1).3=32
42 - (x + 1).3=9
(x + 1).3=42-9
(x + 1).3=33
x + 1=33:3
x + 1=11
x=11-1
x=10