a)=2

b)=1/3

a,2

b,1/3

Bài 1:

1+2+3+4+5+5+6+7+8+9

=(1+9)+(2+8)+(3+7)+(4+6)+(5+5)

=10+10+10+10+10

=50

Bài 2:

3*2*2*2*10*10*10*10

=3*(2*3)*(10*4)

=3*6*40

=640

hok tốt (đúng chưa vậy)

Bài 1 :

1 + 2 + 3 + 4 + 5 + 5 + 6 + 7 + 8 + 9 

= ( 1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + ( 5 + 5 )

= 10 + 10 + 10 + 10 + 10

= 50

  BÀI 1. TÍNH BẰNG CÁCH THUẬN TIỆN NHẤT 

1+2+3+4+5+5+6+7+8+9 = 

=(1+9)+(2+8) +(3+7)+(4+6)+5

= 10+10+10+10+5

=45

BÀI 2. TÍNH BẰNG CÁCH THUẬN TIỆN NHẤT

3 x 2 x 2 x 2 x 10 x 10 x10 x 10 = 240 000

Giải đấy đủ giúp mình với 

a: =8/15x1/4=2/15

b: \(=\dfrac{5}{3}\cdot\dfrac{4}{5}\cdot\dfrac{6}{7}=\dfrac{24}{21}=\dfrac{8}{7}\)

c: \(=\dfrac{2}{5}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=\dfrac{2}{5}\)

2 năm sau mày sẽ chết do dịch bệnh

\(5\dfrac{3}{4}:3+2\dfrac{1}{4}\times\dfrac{1}{3}-\dfrac{1}{8}=\left(5\dfrac{3}{4}+2\dfrac{1}{4}\right)\times\dfrac{1}{3}-\dfrac{1}{8}\\ =8\times\dfrac{1}{3}-\dfrac{1}{8}=\dfrac{8}{3}-\dfrac{1}{8}=\dfrac{61}{24}\\ ----\\ \dfrac{3}{5}:\dfrac{5}{6}:\dfrac{6}{7}:\dfrac{7}{8}+\dfrac{2}{5}+\dfrac{23}{35}\\ =\dfrac{3}{5}\times\dfrac{6}{5}\times\dfrac{7}{6}\times\dfrac{8}{7}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{18}{25}\times\dfrac{4}{3}+\dfrac{2}{5}+\dfrac{23}{35}=\dfrac{353}{175}\)

1) \(=\left(\frac{3}{5}+\frac{2}{5}\right).\frac{6}{11}\)

\(=1.\frac{6}{11}\)

\(=\frac{6}{11}\)

2)\(\frac{17}{25}.\left(\frac{11}{19}+\frac{6}{19}+\frac{2}{19}\right)\)

\(=\frac{17}{25}.1\)

\(=\frac{17}{25}\)

2.\(\frac{17}{25}.\frac{11}{19}+\frac{17}{25}.\frac{6}{19}+\frac{17}{25}.\frac{2}{19}=\frac{17}{25}\left(\frac{11}{19}+\frac{6}{19}+\frac{2}{19}\right)\\ =\frac{17}{25}.1\\ =\frac{17}{25}\)

1,

a,=4/7:4/9.3

=9/7.3

=27/7

b,=(7/11+4/11).5/6

=1.5/6

=5/6

`(6/7-2/7):4/9xx3=4/7xx9/4xx3=[4xx9xx3]/[7xx4]=27/7`

`7/11xx5/6+4/11xx5/6=(7/11+4/11)xx5/6=11/11xx5/6=5/6`

1) 3/9 + 5/9 = 8/9

2) 1/2 x 2/3 x 3/4 x 4/5

= 1/5

(1-1/2)×(1-1/3)×(1-1/4)×(1-1/5)×1-1/6=1/2×2/3×3/4×4/5×5/6=1/6