1. = 13

2. = 346

3.= -69

4. = -2600

5. -2150

300

465 

a,=3/13.17/29.29/34

=3/13.1/2

=3/26

b,=(4/21+25/42).19/33

=11/14.19/33

=19/42

`a, = 3/13 xx (17/29 xx 29/34)`

`= 3/13 xx 1/2`

`= 3/26`.

`b, = 19/33(4/21 + 25/42)`

`= 19/33 xx ( 33/42 )`

`= 19/42`

12) 17 – 11 – 14 – (-39)

=17-11-14+39

=6-14+39

=-8+39

=31

13) −127 - 18.( 5 - 6)

=-127-18.1

=-145
14) 100 + (+430) + 2145 + (-530)

=530+2145-530

=(530-530)+2145

=0+2145

=2145
15) (+12).13 + 13.(-22)

=13.[12+(-22)]

=13.(-10)

=-130
16) {[14 : (-2)] + 7} : 2012

={-7+7}:2012

=0:2012

=0
17) 13 – 18 – (- 42) - 15

=13-18+42-15

=-5+42-15

=37-15

=22
18) 369 – 4[(-5) + 4.(-8)]

=369-4[-5+(-32)]

=369-4(-37)

=369+148

=517
19) (-12).(-13) +13.(-29)

=12.13+13.(-29)=13.[12+(-29)]=13.(-17)=-221

20) 125 – 4[ 3 – 7.(-2) ]

=125-4[3+14]

=125-4.17

=125-68

=57
21) (-14).9 – 13.(-9)

=(-14).9+13.9

=9.[-14+13]

=9.(-1)

=-9

âm 9 nha bạn
 

áp dụng kiến thức tính nhanh ý

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50=1275

=1275

=1245

0.5

giúp mình cách giải với

$\frac{3}{13}\times \frac{17}{29})\times \frac{29}{34}$

     $=\frac{3}{13}\times \frac{17}{29}\times \frac{29}{34}$

     $=\frac{3\times 17\times 29}{13\times 29\times 34}$

     $=\frac{3\times 17\times 29}{13\times 29\times 2\times 17}$

     $=\frac{3}{13\times 2}$

     $=\frac{3}{26}$

     $\frac{4}{21}\times \frac{19}{33}+\frac{25}{42}\times \frac{19}{33}$

     $=\frac{19}{33}\times (\frac{4}{21}+\frac{25}{42})$

     $=\frac{19}{33}\times (\frac{8}{42}+\frac{25}{42})$

     $=\frac{19}{33}\times \frac{33}{42}$

     $=\frac{19\times 33}{33\times 42}$

     $=\frac{19}{42}$