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2,
a) \(315-\left(135-x\right)=215\)
\(\Rightarrow135-x=315-215\)
\(\Rightarrow135-x=100\)
\(\Rightarrow x=135-100\)
\(\Rightarrow x=35\)
b) \(x-320:32=25\cdot16\)
\(\Rightarrow x-10=5^2\cdot4^2\)
\(\Rightarrow x-10=20^2\)
\(\Rightarrow x-10=400\)
\(\Rightarrow x=410\)
c) \(3\cdot x-2018:2=23\)
\(=3\cdot x-1009=23\)
\(\Rightarrow3\cdot x=1032\)
\(\Rightarrow x=1032:3\)
\(\Rightarrow x=344\)
d) \(280-9\cdot x-x=80\)
\(\Rightarrow280-x\cdot\left(9+1\right)=80\)
\(\Rightarrow280-10\cdot x=80\)
\(\Rightarrow10\cdot x=280-80\)
\(\Rightarrow10\cdot x=200\)
\(\Rightarrow x=20\)
e) \(38\cdot x-12\cdot x-x\cdot16=40\)
\(\Rightarrow x\cdot\left(38-12-16\right)=40\)
\(\Rightarrow x\cdot10=40\)
\(\Rightarrow x=40:10\)
\(\Rightarrow x=4\)
\(\text{35 + (–47) – |–12|}\)
\(=-12-12\)
\(=-24\)
\(\text{(–15) – 70 : (–14) + (–32) . (–2)}\)
\(=-15+5+64\)
\(=-10+64\)
\(=54\)
\(\text{ 15 – 12 . (-3)^2 – 135 : |–15|}\)
\(=15-12.9-135:15\)
\(=15-108-9\)
\(=-102\)
Tính hợp lý:
\(\text{ –24 . 78 + 24(–35) – 24(–13)}\)
\(=24.\left(-78+\left(-35\right)-\left(-13\right)\right)\)
\(=24.\left(-100\right)\)
\(=-2400\)
học tốt
\(17.\left(15-16\right)+16.\left(17-20\right)\)
\(=17.15-17.16+16.17-16.20\)
\(=17.15-16.20+\left(17.16-17.16\right)\)
\(=255-320+0\)
\(=-65\)
CHÚC BN HỌC TỐT!!!!!
a) 3/7 + 4/9 + 4/7 + 5/9
= ( 3/7 + 4/7 ) + ( 4/9 + 5/9 )
= 7/7 + 9/9
= 1 + 1
= 2
b)1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45
= 1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5
= ( 1/5 + 9/5 ) + ( 2/5 + 8/5 ) + (7/5 + 3/5 ) + ( 4/5 + 6/5 ) + 5/5
= 2 + 2 + 2 + 2 + 1
= 2 x 4 + 1
= 8 +1
= 9
c) 1/8 + 1/12 + 3/8 + 5/12
= ( 1/8 + 3/8 ) + ( 1/12 + 5/12)
= 4/8 + 6/12
= 1/2 + 1/2
= 2/4 = 1/2
mỏi tay rồi
1. Thực hiện phép tính bằng cách hợp lí :
a) (-46) + (-125) + 46 + 25 = [(-46)+46] + [(-125)+25]
= 0+(-100) = -100
b) 25.(-15) + 25.(-5) + (-20).75 = 25.[(-15)+(-5)] + (-20).75
= 25.(-20) + (-20).75 = (-20).(25+75) = (-20).100 = -2000
c) (-151)+(-37)+(-42)+(-63)+142 =(-151)+[(-37)+(-63)]+[(-42)+142]
= (-151) + [(-100) + 100] = -151
d)32+(-149)+(-311)+(-89)+(-51) = 32+[(-149)+(-51)] + [(-311)+(-89)]
= 32+[(-200)+(-400)] = 32+(-600) = -568
e)-65.(87-17)-87.(17-65) = (-65).87 - (-65).17 - 87.17 + 87.65
= (-65).87 + 65.17 - 87.17 + 87.65 = [(-65).87+87.65] + 65.(17-87)
= 65.(-70) = -4550
g) -43.(53-16) - 53.(16-43) = (-43).53 - (-43).16 - 53.16 + 53.43
= (-43).53 + 43.16 - 53.16 + 53.43 = [(-43).53+53.43] + 16.(43-53)
= 16.(-10) = -160
a. 32 + (–49) – |–15|
= 32 - 49 - 15
= -32
b. (–12) – 80 : (–16) + (–25) . (–3)
= - 12 + 5 + 75
= 68
c. 17 – 15 . (–2)2 – 144 : |–16|
= 17 - 15.4 - 144 : 16
= 17 - 60 - 9
= -52
a, 32 + (-49) -|-15|
= -17 - 15
= -32
b, (-12) - 80 : (-16) + (-25) . (-3)
= (-12) - (-5) + 75
= -7 + 75
= 68
c, 17 - 15 . (-2)2 - 144 :|-16|
= 17 - 15. 4 - 144 : 16
= 17 - 60 - 9
= -43 - 9
= -52
d, -35 . 54 + 32.(-63) - 32(-17)
= -1890 + 32. [-63 - (-17)]
= -1890 + 32. (-46)
= -1890 + (-1472)
= -3362.
Tham khảo nha!!!