2

100

a) 25 + 69 + 75 + 11

= (25 + 75) + (69 + 11)

= 100 + 80

= 180

b) 64 x 867 + 36 x 867

= (64 + 36) x 867 

= 100 x 867

= 86700

c) 25 x 989 x 4 + 25

= 25 x 4 x 989 + 25

= 100 x 989 + 25

= 98900 + 25

= 98925

a)25 + 69 + 75 + 11 

=(25 + 75) + (69 + 11)

=100 + 80

=180

b)64 * 867 + 36 * 867

=(64 + 36) * 867

=100 * 867

=86700

c)25 * 989 * 4 +25

=25*3956+25

=25*(3956+1)

=25*3957

=98925

(25+75)+(69+11)

c1                           {3/4+1/2}*5/7

                               =5/4*5/7

                               =25/28 

c2                          {3/4+1/2}*5/7

                               = 3/4*5/7+1/2*5/7

                               =15/28+5/14

                               =25/28

C1: 2/3 x (4/5 x 5/6) = 2/3 x 2/3 = 4/9

C2: (2/3 x 4/5) x 5/6 = 8/15 x 5/6 = 4/9

\(\frac{2}{3}x\frac{4}{5}x\frac{5}{6}\)

\(=\frac{8}{15}x\frac{5}{6}\)

\(=\frac{4}{9}\)

Đố ai tìm được.

\(\frac{3}{5}\times\frac{7}{21}+\frac{7}{21}\times\frac{2}{5}=\frac{7}{21}\times\left(\frac{3}{5}+\frac{2}{5}\right)=\frac{1}{3}\times\left(\frac{3}{5}+\frac{2}{5}\right)=\frac{1}{3}\times1=\frac{1}{3}\)

   Học tốt !

\(\frac{3}{5}\cdot\frac{7}{21}+\frac{7}{21}+\frac{2}{5}\)

\(=\frac{7}{21}\cdot(\frac{3}{5}+\frac{2}{5})\)

\(=\frac{7}{21}\cdot1=\frac{7}{21}=\frac{1}{3}\)

C1  \(\frac{3}{5}.\frac{7}{21}+\frac{7}{21}.\frac{2}{5}\)

\(=\frac{7}{21}\left(\frac{3}{5}+\frac{2}{5}\right)\)

\(=\frac{7}{21}.1\)

\(=\frac{7}{21}=\frac{1}{3}\)

C2   \(\frac{3}{5}.\frac{7}{21}+\frac{7}{21}.\frac{2}{5}\)

\(=\frac{3.7}{5.21}+\frac{7.2}{21.5}\)

\(=\frac{21}{105}+\frac{14}{105}\)

\(=\frac{35}{105}\)

\(=\frac{7}{21}=\frac{1}{3}\)

\(\frac{36\times45}{6\times5}=\frac{6\times6\times5\times9}{6\times5}=6\times9=54\)

\(\frac{36.45}{6.5}=6.9=54\)
 

\(\frac{36x45}{6x5}=\frac{6x6x5x9}{6x5}=6x9=54\)