5 x 10 + 90 = 70 x ?
tính bằng cách thuận tiện nhất , giải bằng 2 cách khác nhau
10 x 5 + 5 x 10
50 + 10 + 90 + 50 + 30 + 60 + 10 + 70 + 50 + 50
10 x 5 + 5 x 10
c1 : 10 x (5 + 5)
= 10 x 10
= 100
c2 : (10 + 10) x 5
= 20 x 5
= 100
50 + 10 + 90 + 50 + 30 + 60 + 10 + 70 + 50 + 50
c1 : (50 + 50) + (10 + 90) + (30 + 60 + 10) + (50 + 50) + 70
= 100 + 100 + 100 + 100 + 70
= 100 x 4 + 70
= 400 + 70
= 470
c2: 50 x 4 + (10 + 90) + (70 + 30) + (60 + 10)
= 200 + 100 + 100 + 70
= 200 + 100 x 2 + 70
= 200 + 200 + 70
= 200 x 2 + 70
= 400 + 70 = 470
Tìm x biết: \(\frac{x+10}{90}+\frac{x+20}{80}+\frac{x+30}{70}+\frac{x+40}{60}+\frac{x+50}{50}=-5\)
\(\frac{x+10}{90}+\frac{x+20}{80}+\frac{x+30}{70}+\frac{x+40}{60}+\frac{x+50}{50}=-5\)
<=> \(\frac{x+10}{90}+1+\frac{x+20}{80}+1+\frac{x+30}{70}+1+\frac{x+40}{60}+1+\frac{x+50}{50}+1=0\)
<=> \(\frac{x+100}{90}+\frac{x+100}{80}+\frac{x+100}{70}+\frac{x+100}{60}+\frac{x+100}{50}=0\)
<=> \(\left(x+100\right)\left(\frac{1}{90}+\frac{1}{80}+\frac{1}{70}+\frac{1}{60}+\frac{1}{50}\right)=0\)
<=> x + 100 = 0
<=> x = -100
Vậy x = -100
Tính nhẩm:
80 + 10 = 30 + 40 = 80 + 5 =
90 - 80 = 70 - 30 = 85 - 5 =
90 - 10 = 70 - 40 = 85 - 80 =
80 + 10 = 90 30 + 40 = 70 80 + 5 = 85
90 - 80 = 10 70 - 30 = 40 85 - 5 = 80
90 - 10 = 80 70 - 40 = 30 85 - 80 = 5
80+10=90 30+40=70 80+5=85
90-80=10 70-30=40 85-5=80
90-10=80 70-40=30 85-80=5
80 + 10 = 90 30 + 40 = 70 80 + 5 = 85
90 - 80 = 10 70 + 30 = 90 85 - 5 = 80
90 - 10 = 80 70 - 40 = 30 85 - 80 = 5
Tìm x biết:
2 x X +68 = 126
3 x X -24 = 90
84 - 4 x X =16
(5 x X + 10 ) + 35 = 70
(6 x X - 18) - 42 =12
( 2 x X - 4 ) + 24
45 - ( 3 x X - 9 ) = 15
60 + (10 x X - 40 ) = 90
145 - (5 x X + 15 ) = 65
84 - ( 2 x X - 8 ) = 46
2 x X + 68 = 126
2 x X = 126 - 68
2 x X = 58
x = 58 : 2
x = 29
a) \(2\times x+68=126\)
\(\Rightarrow2\times x=58\)
\(\Rightarrow x=29\)
b) \(3\times x-24=90\)
\(\Rightarrow3\times x=123\)
\(\Rightarrow x=41\)
c) \(84-4\times x=16\)
\(\Rightarrow4\times x=84-16=68\)
\(\Rightarrow x=17\)
d) \(\left(5\times x+10\right)+35=70\)
\(\left(5\times x+10\right)=70-35\)
\(\Rightarrow5\times x+10=35\)
\(\Rightarrow5\times x=25\)
\(\Leftrightarrow x=5\)
e) Tương tự d
f) Thiếu kết quả của đề
g) \(45-\left(3\times x-9\right)=15\)
\(\Rightarrow(3\times x-9)=45-15\)
\(\Rightarrow3\times x-9=30\)
\(\Rightarrow3\times x=39\)
\(\Rightarrow x=13\)
-- Các câu còn lại tương tự câu g
Tính nhẩm:
a) 10 x 7 20 x 4 40 x 2 30 x 3
b) 60 : 2 90 : 3 70 : 7 40 : 2
a) 10 x 7 = ? Nhẩm: 1 chục x 7 = 7 chục 10 x 7 = 70 20 x 4 = ? Nhẩm: 2 chục x 4 = 8 chục 20 x 4 = 80 40 x 2 = ? Nhẩm: 4 chục x 2 = 8 chục 40 x 2 = 80 30 x 3 = ? Nhẩm: 3 chục x 3 = 9 chục 30 x 3 = 90 | b) 60 : 2 = ? Nhẩm: 6 chục : 2 = 3 chục 60 : 2 = 30 90 : 3 = ? Nhẩm: 9 chục : 3 = 3 chục 90 : 3 = 30 70 : 7 = ? Nhẩm: 7 chục : 7 = 1 chục 70 : 7 = 10 40 : 2 = ? Nhẩm: 4 chục : 2 = 2 chục 40 : 2 = 20 |
Tính giá trị của biểu thức:
a) 90 – ( 30 – 20) = ..........................
= ..........................
90 – 30 – 20 = ..........................
= ..........................
b) 100 – (60 + 10) = ..........................
= ..........................
100 - 60 + 10 = ..........................
= ..........................
c) 135 – (30 + 5) = ..........................
= ..........................
135 – 30 – 5 = ..........................
= ..........................
d) 70 + (40 – 10) = ..........................
= ..........................
70 + 40 – 10 = ..........................
= ..........................
a) 90 – ( 30 – 20) = 90 – 10
= 80
90 – 30 – 20 = 60 - 20
= 40
b) 100 – (60 + 10) = 100 – 70
= 30
100 - 60 + 10 = 40 + 10
= 50
c) 135 – (30 + 5) = 135 – 35
= 100
135 – 30 – 5 = 105 – 5
= 100
d) 70 + (40 – 10) = 70 + 30
= 100
70 + 40 – 10 = 110 -10
= 100
nguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
nguuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
Tìm giá trị nhỏ nhất:
A=/2-2/ + /y +5/ -10
B=(X-8)^2+2019
C=90 - /20-X/- /70 +Y/
b) Ta có :
\(\left(x-8\right)^2\ge0;\forall x\)
\(\Rightarrow\left(x-8\right)^2+2019\ge2019;\forall x\)
Hay\(B\ge2019;\forall x\)
Dấu "=" xảy ra \(\Leftrightarrow\left(x-8\right)^2=0\)
\(\Leftrightarrow x=8\)
Vậy MIN B=2019 \(\Leftrightarrow x=8\)
c) Vì \(\hept{\begin{cases}-|20-x|\le0;\forall x\\-|70+y|\le0;\forall y\end{cases}}\)
\(\Rightarrow-|20-x|-|70+y|\le0;\forall x,y\)
\(\Rightarrow90-|20-x|-|70+y|\le90-0;\forall x,y\)
Hay \(C\le90;\forall x,y\)
Dấu "=" xảy ra \(\Leftrightarrow\hept{\begin{cases}|20-x|=0\\|70+y|=0\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}x=20\\y=-70\end{cases}}\)
Vậy MAX C=90 \(\Leftrightarrow\hept{\begin{cases}x=20\\y=-70\end{cases}}\)
A=|2-2|+|y+5|-10
\(=\left|y+5\right|-10\ge-10\forall x\in R\)
Dấu "=" xảy ra <=> \(\left|y+5\right|=0\Leftrightarrow y+5=0\Leftrightarrow y=-5\)
Vậy Amin =-10 tại y=-5
A=(1+2)x(3000+456) B=(2000+5)x(10-1)
C=(101-1)x(5000+40+7) D=(5000+47)x(90+10)
E=(3000+400+50+6)x3 G=(2+3+4)x(1935+70)
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
Tính rồi viết kết quả dưới dạng số thập phân:
a) 1/10 + 4/20 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 64/80 + 81/90
b: ( 4/5 x 3/8 + 4/5 x 5/8 - 4/5 x 7/8 ) : 1/2