Bài1.Tính nhanh:4/7 x 8/13 + 8/13 x 3/7
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Tính nhanh:
a)11/7 x 8/13 + 8/13 x 3/7 + 8/13
b)5/7 x 8/13 + 8/13 x 9/7 - 8/13
c)156 x 199 - 57 x 199 - 199
a.11/7.8/13+8/13.3/7+8/13
=8/13.(11/7+3/7+1)
=8/13.3
=24/13
b.5/7.8/13+8/13.9/7-8/13
=8/13.(5/7+9/7-1)
=8/13.1
=8/13
c.157.199-56.199-199
=199.(157-56-1)
=199.100
19900
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tính nhanh
a) 12/13 + 2/7 + 8/13 + 6/13 + 5/7 =
b) (1 - 1/2) x (1 - 1/3) x ( 1 - 1/4) x (1 - 1/5) =
câu a) lấy mẫu số chung cộng với nhau
câu b) lấy 1 để ngoài nhân r 1/2-1/3 rồi tương tự
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Tính nhanh: LƯU Ý tất cả số dưới đây đều là phân số
1,1/8 x 2/5 + 3/5 + 1/8
2,( -1)/15 x 2/5 + (-5)/3 x (-1)/13
3,4/9 : 11/6 + 5/9 x 6/11
4,5/19 x 7/13 + 7/19 x 8/13 - 3 x 7/19
5, 2/7 x 4/23 - 2/7 x 27/23 + 2/7
6,3/8 x 3/7 +3/8 x 4/7 + 11/8
7,-5/27 : 6/11 - 16/11 x 5/27 - 5/27
8, 5/16 x 7/8 - 5/16 x 1/8 + 10/8 :16/5
9,1/3 x 39/17 - 129/3 x 1/17
10,5/2 : 23/3 - 3/2 x 7/23
2: \(=\dfrac{-2}{75}+\dfrac{5}{39}=\dfrac{33}{325}\)
3: \(=\dfrac{6}{11}\left(\dfrac{4}{9}+\dfrac{5}{9}\right)=\dfrac{6}{11}\)
4: \(=\dfrac{7}{19}\left(\dfrac{5}{13}+\dfrac{8}{13}-1\right)=-2\cdot\dfrac{7}{19}=-\dfrac{14}{19}\)
5: \(=\dfrac{2}{7}\left(\dfrac{4}{23}-\dfrac{27}{23}+1\right)=0\)
6: \(=\dfrac{3}{8}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)+\dfrac{11}{8}=\dfrac{3}{8}+\dfrac{11}{8}=\dfrac{14}{8}=\dfrac{7}{4}\)
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Tính bằng cách thuận tiên nhất:1):(3/4 x 5/97 + 1/9 x 13/47) x (1/5 - 7/25 x 5/7)2): 8/17 x 4/15 + 8/17 x 22/15 - 8/15 x 9/173): 2021/2 x 1/3 + 4042/4 x 1/5 + 6063/3 x 22/154); 4/7 x 2/13 + 8/13 :7/4 + 4/7 : 13/2 + 4/7 x 1/135): 2022 x 2021 - 1/ 2021 + 2022 x 20206): 18 x 123 + 9 x 4567 x 2 + 3 x 5310 x 6 / (2 + 4 + 6 + 8 + ...+20 + 22) + 487): A 2021 x 2021 x 202020 - 2020 x 2020 x 20212021 / 2020 x 201920...
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Tính bằng cách thuận tiên nhất:
1):(3/4 x 5/97 + 1/9 x 13/47) x (1/5 - 7/25 x 5/7)
2): 8/17 x 4/15 + 8/17 x 22/15 - 8/15 x 9/17
3): 2021/2 x 1/3 + 4042/4 x 1/5 + 6063/3 x 22/15
4); 4/7 x 2/13 + 8/13 :7/4 + 4/7 : 13/2 + 4/7 x 1/13
5): 2022 x 2021 - 1/ 2021 + 2022 x 2020
6): 18 x 123 + 9 x 4567 x 2 + 3 x 5310 x 6 / (2 + 4 + 6 + 8 + ...+20 + 22) + 48
7): A= 2021 x 2021 x 202020 - 2020 x 2020 x 20212021 / 2020 x 20192019
1) Ta có: \(\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{7}{25}\cdot\dfrac{5}{7}\right)\)
\(=\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{1}{5}\right)\)
=0
2) Ta có: \(\dfrac{8}{17}\cdot\dfrac{4}{15}+\dfrac{8}{17}\cdot\dfrac{22}{15}-\dfrac{8}{15}\cdot\dfrac{9}{17}\)
\(=\dfrac{8}{17}\left(\dfrac{4}{15}+\dfrac{22}{15}-\dfrac{9}{15}\right)\)
\(=\dfrac{8}{17}\cdot\dfrac{15}{15}=\dfrac{8}{17}\)
3) Ta có: \(\dfrac{2021}{2}\cdot\dfrac{1}{3}+\dfrac{4042}{4}\cdot\dfrac{1}{5}+\dfrac{6063}{3}\cdot\dfrac{22}{15}\)
\(=\dfrac{2021}{2}\left(\dfrac{1}{3}+\dfrac{1}{5}\right)+2021\cdot\dfrac{22}{15}\)
\(=\dfrac{2021}{2}\cdot\dfrac{8}{15}+\dfrac{2021}{2}\cdot\dfrac{44}{15}\)
\(=\dfrac{2021}{2}\cdot\dfrac{52}{15}\)
\(=\dfrac{52546}{15}\)
4) Ta có: \(\dfrac{4}{7}\cdot\dfrac{2}{13}+\dfrac{8}{13}:\dfrac{7}{4}+\dfrac{4}{7}:\dfrac{13}{2}+\dfrac{4}{7}\cdot\dfrac{1}{13}\)
\(=\dfrac{4}{7}\left(\dfrac{2}{13}+\dfrac{8}{13}+\dfrac{2}{13}+\dfrac{1}{13}\right)\)
\(=\dfrac{4}{7}\)
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Tính nhanh
4/7+46/13+25/8+3/7-1/8-7/13
\(\dfrac{4}{7}+\dfrac{46}{13}+\dfrac{25}{8}+\dfrac{3}{7}-\dfrac{1}{8}-\dfrac{7}{13}\)
\(=\left(\dfrac{4}{7}+\dfrac{3}{7}\right)+\left(\dfrac{46}{13}-\dfrac{7}{13}\right)+\left(\dfrac{25}{8}-\dfrac{1}{8}\right)\)
\(=1+3+3=7\)
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thực hiện phép tính(tính nhanh nếu có thể):
a)2/13 x 5/9+3/13 x 9/11+11/13
b)5/7 x -3/11+-5/7 x 8/11+9/7
Tính một cách hợp lí :
a) -3/8-13/65+3/8
b) (-13/7-4/9)-(-10/7-4/9)
C) 17 1/3 x(-3/7)+3 2/3 x(-3/7)
\(a.\dfrac{-3}{8}-\dfrac{13}{65}+\dfrac{3}{8}=\left(\dfrac{3}{8}-\dfrac{3}{8}\right)-\dfrac{13}{65}=-\dfrac{13}{65}\)
\(b.\left(\dfrac{-13}{7}-\dfrac{4}{9}\right)-\left(-\dfrac{10}{7}-\dfrac{4}{9}\right)=\dfrac{-13}{7}-\dfrac{4}{9}+\dfrac{10}{7}+\dfrac{4}{9}\\ =\left(\dfrac{-13}{7}+\dfrac{10}{7}\right)+\left(\dfrac{4}{9}-\dfrac{4}{9}\right)=-\dfrac{3}{7}\)
\(c.17\dfrac{1}{3}\cdot\left(\dfrac{-3}{7}\right)+3\dfrac{2}{3}\cdot\left(\dfrac{-3}{7}\right)=\dfrac{-3}{7}\cdot\left(17\dfrac{1}{3}+3\dfrac{2}{3}\right)\\ =\dfrac{-3}{7}\cdot\left(\dfrac{52}{3}+\dfrac{11}{3}\right)=\dfrac{-3}{7}\cdot21=-9\)
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bài1: tính nhanh
a, 89 + ( -36 ) + ( -8 ) + 29 + 15 + ( -34 )
b, -195 . 56 -43 . 195 - 195
c, 135 . ( -12 + 147 ) - 147 . ( 135 - 12 )
bài 2 : tìm x
a, 3-(17-x) = -12
b, -26-(x-7)= 0
c, /x+3/-7=13
d, /x-7/+15=23
e, (x+2)(x+3)=0
g, (x-1)( x^2+1)=0
b) -26 - ( x - 7 ) = 0
x - 7 = -26 - 0
x - 7 = -26
x = -26 + 7
x = -19
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Bài 2 :
a) 3 - ( 17 - x ) = -12
( 17 - x ) = 3 - ( -12 )
( 17 - x ) = 15
x = 17 - 15
x = 2
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b) -26 - ( x - 7)=0
x - 7 = -26 -0
x - 7 = -26
x = -26 + 7
x = -19
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Xem thêm câu trả lời
tính nhanh : A, \(\dfrac{7,2:2\cdot28,6+1,43\cdot2\cdot64}{13+5+7+...+49-339}\)
tìm x : B, 2+( \(\dfrac{3}{2}\)+ x - \(\dfrac{5}{8}\) ) : \(\dfrac{13}{4}\)=6
a: Sửa đề; \(A=\dfrac{7.2:2\cdot28.6+1.43\cdot2\cdot64}{1+3+5+7+...+49-339}\)
\(=\dfrac{3.6\cdot28.6+2.86\cdot64}{1+3+5+...+49-339}\)
\(=\dfrac{2.86\left(64+36\right)}{25^2-339}=\dfrac{286}{286}=1\)
b: =>2(x+7/8)=6*13/4=78/4=39/2
=>x+7/8=39/4
=>x=71/8
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