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- Tính giá trị biểu thức:
a) (2/5 x 25/29) + (3/5 x 25/29)
= (50/145) + (75/145)
= 125/145
b) (5/2 x 3/7) - (3/14 : 6/7)
= 15/14 - (3/14 x 7/6)
= 15/14 - 1/2
= (30/28) - (14/28)
= 16/28
= 4/7
c) (15/4 : 5/12) - (6/5 : 11/15)
= (15/4 x 12/5) - (6/5 x 15/11)
= 180/20 - 90/55
= 9 - 18/11
= (99/11) - (18/11)
= 81/11
= 7 4/11
- Tính giá trị biểu thức:
a) (2/3) + (20/21 x 3/2 x 7/5)
= 2/3 + (60/210)
= 2/3 + 2/7
= (14/21) + (6/21)
= 20/21
b) (5/17 x 21/32 x 47/24 x 0)
= 0
c) (11/3 x 26/7) - (26/7 x 8/3)
= (286/21) - (208/21)
= 78/21
= 3 9/21
= 3 3/7
- Tìm x:
a) (25/8) : x = 5/16
=> (25/8) x (16/5) = x
=> 4 = x
b) x + (7/15) = 6/15
=> x = (6/15) - (7/15)
=> x = -1/15
c) x : (28/49) = 7/12
=> x x (49/28) = 7/12
=> x = (7/12) x (28/49)
=> x = 1/2
- Tìm x:
a) 6 x x = (5/8) : (3/4)
=> 6x = (5/8) x (4/3)
=> 6x = 20/24
=> 6x = 5/6
=> x = (5/6) / 6
=> x = 5/36
câu,b,không,đủ,thông,tin,nhan,bạn.
\(=25\%+25\%\times38+25\%\times50+25\%\times11\)
\(=25\%\times\left(1+38+50+11\right)=25\%\times100=25\)
4.Tính bằng cách thuận tiện
a)19,75 x 0,4 x 2,5
= 19,75 x ( 0 ,4 x 2,5)
= 19,75 x 1
= 19,75
b) 9, 67 x 80 x 1,25
= 9,67 x ( 80 x 1,25)
= 9,67 x 100
= 967
c) 49,6 x 0,5 x 4
= 49,6 x ( 0,5 x 4)
= 49,6 x 2
= 99,2
d) 0,25 x 0,2 x 4 x 50
= ( 0,25 x 4 ) x ( 0,2 x 50)
= 1 x 10
= 10
5.Tính giá trị biểu thức :
140 : 2,8 x 6,85 – 2,3
= 50 x 6,85 - 2,3
= 342,5 - 2,3
= 340,2
# HOK TỐT #
\(a)19,75\times\left(0,4\times2,5\right)\)
\(=19,75\times1\)
\(=19,75\)
\(\text{b) 9, 67 x 80 x 1,25}\)
\(\text{ =9, 67 x(80 x 1,25)}\)
\(\text{= 9, 67 x 100}\)
\(=967\)
\(\text{c) 49,6 x 0,5 x 4}\)
\(=\text{49,6 x (0,5 x 4})\)
\(\text{=49,6 x 2}\)
\(=99,2\)
\(\text{d) 0,25 x 0,2 x 4 x 50}\)
\(\text{=(0,25 x 4) x (0,25 x 50)}\)
\(=1\times12,5\)
\(=12,5\)
a;
c; \(\dfrac{1}{10}\) + \(\dfrac{4}{20}\) + \(\dfrac{9}{30}\)+\(\dfrac{16}{40}+\dfrac{25}{50}+\dfrac{36}{60}+\dfrac{49}{70}+\dfrac{64}{80}+\dfrac{81}{90}\)
= \(\dfrac{1}{10}+\dfrac{2}{10}+\dfrac{3}{10}+\dfrac{4}{10}+\dfrac{5}{10}+\dfrac{6}{10}+\dfrac{7}{10}+\dfrac{8}{10}+\dfrac{9}{10}\)
= \(\dfrac{1+2+3+4+5+6+7+8+9}{10}\)
= \(\dfrac{\left(1+9\right)+\left(2+8\right)+\left(3+7\right)+\left(4+6\right)+5}{10}\)
= \(\dfrac{10+10+10+10+5}{10}\)
= \(\dfrac{\left(10+10+10+10\right)+5}{10}\)
= \(\dfrac{10\times4+5}{10}\)
= \(\dfrac{45}{10}\)
= \(\dfrac{9}{2}\)
Bài 1:
a; (\(\dfrac{1}{4}\)\(x\) - \(\dfrac{1}{8}\)) x \(\dfrac{3}{4}\) = \(\dfrac{1}{4}\)
\(\dfrac{1}{4}x\) - \(\dfrac{1}{8}\) = \(\dfrac{1}{4}\) : \(\dfrac{3}{4}\)
\(\dfrac{1}{4}\)\(x\) - \(\dfrac{1}{8}\) = \(\dfrac{1}{4}\) x \(\dfrac{4}{3}\)
\(\dfrac{1}{4}x\) - \(\dfrac{1}{8}\) = \(\dfrac{1}{3}\)
\(\dfrac{1}{4}x\) = \(\dfrac{1}{3}\) + \(\dfrac{1}{8}\)
\(\dfrac{1}{4}\) \(x\)= \(\dfrac{8}{24}\) + \(\dfrac{11}{24}\)
\(\dfrac{1}{4}x=\dfrac{11}{24}\)
\(x=\dfrac{11}{24}:\dfrac{1}{4}\)
\(x=\dfrac{11}{24}\times4\)
\(x=\dfrac{11}{6}\)
b; \(\dfrac{12}{5}:x\) = \(\dfrac{14}{3}\) x \(\dfrac{4}{7}\)
\(\dfrac{12}{5}\) : \(x\) = \(\dfrac{8}{3}\)
\(x\) = \(\dfrac{12}{5}\) : \(\dfrac{8}{3}\)
\(x\) = \(\dfrac{12}{5}\) x \(\dfrac{3}{8}\)
\(x\) = \(\dfrac{9}{10}\)
Bằng46080000000 chúc bạn hok tốt mình tính nhẩm bằng đầu đó nha
Lời giải:
\((50\times 60\times 70\times 80):(15\times 25\times 28\times 20)\\ =(50:25)\times (60:15)\times (70:28)\times (80:20)\\ =2\times 4\times \frac{5}{2}\times 4=80\)