1) 1/5 . 5/4 + 1/5 . 5/4

= (1/5 + 1/5) . 5/4

= 1/5 . 5/4

= 1/4

2)tự làm

1.\(\frac{1}{5}\times\frac{5}{4}+\frac{1}{5}\times\frac{5}{4}\)

\(=\frac{1}{5}\times\frac{5}{4}\times2\)

\(=\frac{1\times5\times2}{5\times4}\)

\(=\frac{1}{2}\)

2.\(\frac{7}{6}\times\frac{2}{5}-\frac{1}{3}\times\frac{2}{5}+\frac{5}{6}\times\frac{2}{5}\)

\(=\frac{2}{5}\times\left(\frac{7}{6}-\frac{1}{3}+\frac{5}{6}\right)\)

\(=\frac{2}{5}\times\left(\frac{7}{6}-\frac{2}{6}+\frac{5}{6}\right)\)

\(=\frac{2}{5}\times\frac{5}{3}\)

\(=\frac{2}{3}\)

\(\frac{1}{5}x\frac{5}{4}+\frac{1}{5}x\frac{5}{4}=\frac{1}{5}x\left(\frac{5}{4}+\frac{5}{4}\right)=\frac{1}{5}x\frac{10}{4}=\frac{10}{20}=\frac{1}{2}\)

\(\frac{7}{6}x2x5-\frac{1}{3}x\frac{2}{5}+\frac{5}{6}x\frac{2}{5}=\frac{7}{6}x\frac{2}{1}x\frac{5}{1}-\frac{1}{3}x\frac{2}{5}+\frac{5}{6}x\frac{2}{5}=\frac{70}{6}-\frac{2}{15}+\frac{10}{30}\)          

                                                                                                                            \(=\frac{350}{30}-\frac{4}{30}+\frac{10}{30}\)

                                                                                                                             \(=\frac{346}{30}+\frac{10}{30}\)

                                                                                                                               \(=\frac{356}{30}\)

Bài số 2 bạn tự rút gọn nha

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

=15/17 x (4/7 + 3/7) - 1/3
=15/17 x 1 - 1/3
=15/17 x (3/3 - 1/3)
=15/17 x 2/3
=30/51

`a)17/7-3/8+4/7-3/5`

`=(17/7+4/7)-(3/8+3/5)`

`=21/7-(15/40+24/40)=3-39/40=120/40-39/40=81/40`

`b)15/11xx2001/2005-3/11xx2001/2005-1/11xx2001/2005`

`=2001/2005xx(15/11-3/11-1/11)`

`=2001/2005xx11/11`

`=2001/2005`

  3/4 x 7/12 + 3/4 x 1/6 + 3/4 x 1/4

=3/4 x (7/12 + 1/6 + 1/4)

=3/4 x (7/12 + 2/12 + 3/12)

=3/4 x 1

=3/4

Chúc học tốt~

3/4x7/12+3/4x1/6+3/4x1/4=3/4x(7/12+1/6+1/4)=3/4x1=3/4

cam on

\(\dfrac{15}{8}\) : \(\dfrac{5}{20}\) - \(\dfrac{7}{8}\) : \(\dfrac{1}{4}\) 

= \(\dfrac{15}{8}\) : \(\dfrac{1}{4}\) - \(\dfrac{7}{8}\) : \(\dfrac{1}{4}\)

= ( \(\dfrac{15}{8}\) - \(\dfrac{7}{8}\)) : \(\dfrac{1}{4}\)

= \(\dfrac{8}{8}\) \(\times\) 4

= 4

Tham khảo nhé bạn :))

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