Bài 1: Tính

\(a.\frac{15}{16}-\frac{7}{16}=\frac{15-7}{16}=\frac{8}{16}=\frac{1}{2}\)

\(b.\frac{7}{4}-\frac{3}{4}=\frac{7-3}{4}=\frac{4}{4}=1\)

\(c.\frac{9}{5}-\frac{3}{5}=\frac{9-3}{5}=\frac{6}{5}\)

\(d.\frac{17}{49}-\frac{12}{49}=\frac{17-12}{49}=\frac{5}{49}\)

Bài 2:Rút gọn rồi tính

\(a.\frac{2}{3}-\frac{3}{9}=\frac{2}{3}-\frac{1}{3}=\frac{2-1}{3}=\frac{1}{3}\)

\(b.\frac{7}{5}-\frac{15}{25}=\frac{7}{5}-\frac{3}{5}=\frac{7-3}{5}=\frac{4}{5}\)

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1)` 2/9 + -3/4 + 5/30= (40+(-135) + 30 )/180 = -65/180 = -13/36`

2) `-7/12 - 11/18=(-21)/36 - 22/36 = -43/36 `

3) `7/8 - (-5)/16=14/16- (-5)/16 = 19/16 `

4) `3/8 - (-9)/10 - 5/16= (30- (-72) -25)/80=77/80`

1)\(\dfrac{2}{9}+\dfrac{-3}{4}+\dfrac{5}{30}\)

\(=\dfrac{2.20}{9.20}+\dfrac{-3.45}{4.45}+\dfrac{5.6}{30.6}\)

\(=\dfrac{40}{180}+\dfrac{-135}{180}+\dfrac{30}{180}\)

\(=\dfrac{40+\left(-135\right)+30}{180}\)

\(=\dfrac{-65}{180}\)

\(=\dfrac{-13}{36}\)

2)\(\dfrac{-7}{12}-\dfrac{11}{18}\)

\(=\dfrac{-7.3}{12.3}-\dfrac{11.2}{18.2}\)

\(=\dfrac{-21}{36}-\dfrac{22}{36}\)

\(=\dfrac{-21-22}{36}\)

\(=\dfrac{-43}{36}\)

3)\(\dfrac{7}{8}-\dfrac{-5}{16}\)

\(=\dfrac{7.2}{8.2}-\dfrac{-5}{16}\)

\(=\dfrac{14}{16}-\dfrac{-5}{16}\)

\(=\dfrac{14-\left(-5\right)}{16}\)

\(=\dfrac{19}{16}\)

4)\(\dfrac{3}{8}-\dfrac{-9}{10}-\dfrac{5}{16}\)

\(=\dfrac{3.10}{8.10}-\dfrac{-9.8}{10.8}-\dfrac{5.5}{16.5}\)

\(=\dfrac{30}{80}-\dfrac{-72}{80}-\dfrac{25}{80}\)

\(=\dfrac{30-\left(-72\right)-25}{80}\)

\(=\dfrac{77}{80}\)

3/8 + 9/2 x 3/4 - 9/4 x 1/3 

= 3/8 + 9/2 x 3/4 - 3/4 

= 3/8 + (9/2 - 1) x 3/4 

= 3/8 + 7/2 x 3/4 

= 3/4 x 1/2 + 7/2 x 3/4 

= 3/4 x ( 1/2 + 7/2 ) 

= 3/4 x 4 

= 3

3/8 + 9/2 x 3/4 - 9/4 x 1/3 

= 3/8 + 9/2 x 3/4 - 3/4 

= 3/8 + (9/2 - 1) x 3/4 

= 3/4 x 1/2 + 7/2 x 3/4 

= 3/4 x ( 1/2 + 7/2) 

= 3/4 x 4

= 3

2/9+3/9+4/9+5/9+6/9+7/9

=2+3+4+5+6+7/9

=27/9

=3

1/6+4/9+5/6+11/16+5/9+5/16

=1/6+5/6+4/9+5/9+11/16+5/16

=1+1+1=3

hok tốt ~

Phương pháp giải:

Tính nhẩm các số rồi điền kết quả vào chỗ trống.

Lời giải chi tiết:

Tính nhẩm:

\(\frac{15^9.16^4}{12^9.125^3}=\frac{\left(3.5\right)^9.\left(2^4\right)^4}{\left(3.4\right)^9.\left(5^3\right)^3}=\frac{3^9.5^9.2^{16}}{3^9.4^9.5^9}=\frac{2^{16}}{4^9}=\frac{2^{16}}{\left(2^2\right)^9}=\frac{2^{16}}{2^{18}}=\frac{1}{4}\)

`39/16 : 5/8 - 7/16 : 5/8`

`=39/16 xx 8/5- 7/16 xx 8/5`

`=8/5 xx (39/16 - 7/16)`

`= 8/5 xx2`

`= 16/5`

__

` 4/3 xx 9/8 - 4/3 xx 3/8`

`=4/3 -(9/8 - 3/8)`

`= 4/3 xx 3/4`

`=1`

\(a,\\ \dfrac{39}{16}:\dfrac{5}{8}-\dfrac{7}{16}:\dfrac{5}{8}\\ =\dfrac{39}{16}\cdot\dfrac{8}{5}-\dfrac{7}{16}\cdot\dfrac{8}{5}\\ =\dfrac{8}{5}\cdot\left(\dfrac{39}{16}-\dfrac{7}{16}\right)=\dfrac{8}{5}\cdot2=\dfrac{16}{5}\\ b,\\ \dfrac{4}{3}\cdot\dfrac{9}{8}-\dfrac{4}{3}\cdot\dfrac{3}{8}=\dfrac{3}{2}-\dfrac{1}{2}=1\)

a)

`39/16:5/8-7/16:5/8`

`=(39/16-7/16):5/8`

`=32/16xx8/5`

`=2xx8/5`

`=16/5`

b)

`4/3xx9/8-4/3xx3/8`

`=4/3xx(9/8-3/8)`

`=4/3xx6/8`

`=4/3xx3/4`

`=1`

2. Tính (+5) + ( +4) = 9

3.Tính (- 9) + ( - 1) = -10

4.Tính : 28 + (-15) = 13

5.Tính (-15) + 12 = - 3

6.Tính (-25) + 25 = 0

7.Tính : 13 - 17 = - 4

8.Tính : (-78) - 9 = - 87

9.Tính : ( -24) - ( - 16) = - 8

10.Tính : 17 - (-3) = 20

11.Tính nhanh : (-21) - ( 48 + 52 - 21) = -100

2,  (+5)+(+4)=+9 hoạc 9 cũng được

3,  (-9)+(-1)=-10

4,  28+(-15)=13

5,  (-15)+12=-3

6,  (-25)+25=0

7,  13-17=4

8,   (-78)-9=-87

9,  (-24)-(-16)=-40

10, 17-(-3)=20

11,  (-21+21)-(48-52)=-4

2.  (+5) + ( +4) = 9

3. (- 9) + ( - 1) = -10

4. 28 + (-15) = 13

5. (-15) + 12 = - 3

6. (-25) + 25 = 0

7. 13 - 17 = - 4

8. (-78) - 9 = - 87

9.( -24) - ( - 16) = - 8

10. 17 - (-3) = 20

11. (-21) - ( 48 + 52 - 21) = -100

\(\dfrac{3}{4}-\dfrac{3}{12}=\dfrac{3\times3}{4\times3}-\dfrac{3}{12}=\dfrac{9}{12}-\dfrac{3}{12}=\dfrac{9-3}{12}=\dfrac{6}{12}=\dfrac{1}{2}\\ \dfrac{16}{9}-\dfrac{18}{27}=\dfrac{16}{9}-\dfrac{2}{3}=\dfrac{16}{9}-\dfrac{2\times3}{3\times3}=\dfrac{16}{9}-\dfrac{6}{9}=\dfrac{16-6}{9}=\dfrac{10}{9}\)

9/12 - 3/12 = 3/12

48/27 - 18/27 = 30/27

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