a) 72 + 9 + 8 = ( 72 + 8 ) + 9

= 80 + 9

= 89

b)37 + 18 + 3 = ( 37 + 3 ) + 18

= 40 + 18

= 58

c) 48 + 26 + 4 = 48 + (26 + 4)

= 48 + 30

= 78

d)85 + 99 + 1 = 85 + ( 99 + 1 )

= 85 + 100 = 185

e) 67 + 98 + 33 = ( 67 + 33 ) + 98

= 100 + 98 = 198

a)=4x25x7
   =100x7
   =700
b) =302x(19-9)
   =302x10
   =3020

\(\frac{17}{25}\times\frac{13}{19}+\frac{17}{25}\times\frac{6}{19}\)

\(=\frac{17}{25}\times\left(\frac{13}{19}+\frac{6}{19}\right)\)

\(=\frac{17}{25}\times\frac{19}{19}\)

\(=\frac{17}{25}\times1\)

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

_HT_

\(\dfrac{17}{25}\left(\dfrac{13}{19}+\dfrac{6}{19}\right)\)

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

bấm lộn nha

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

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`

`a)(3/13xx17/29)xx29/34=3/13xx17/29xx29/34=[3xx17xx29]/[13xx19xx17xx2]=3/26`

`b)4/21xx19/33+25/42xx19/33=19/33xx(4/21+25/42)=19/33xx(8/42+25/42)=19/33xx33/42=19/42`

a) 214 × 13 + 214 × 17 = 214 × (13 +17)

= 214 × 30

= 6420

b) 58 × 635 + 48 × 635 = (58 – 48 ) × 635

= 10 × 635

= 6350

c) 4 × 19 × 25 =100 × 19

= 1900

\(\frac{3}{7}x\frac{25}{19}-\frac{1}{7}x\frac{18}{19}\)

\(=\left(\frac{3}{7}-\frac{1}{7}\right)x\left(\frac{25}{19}-\frac{18}{19}\right)\)

\(=\frac{2}{7}x\frac{7}{19}\)

\(=\frac{14}{133}\)

3/7×25/19-2/7×18/19

75/133-36-133

39/133