a) 8 × 5 × 9 = (8 × 5) × 9 = 40 × 9 = 360

b) 6 × 7 × 5 = (6 × 5) × 7= 30 × 7= 210

c) 6 × 4 × 25 = 6 × (4 × 25) = 6 × 100= 600

Tính nhanh :

    9 x 8 x 15 / 12 x 6 x 5 = ( 9 x 6 ) x ( 8 x 5 ) x 15 / 12

                                     =     36     x     40     x 15 / 12

                                     =           1440           x 15 / 12

                                     =               21600 / 17280

                    Đáp số : 21600 / 17280.( mình chưa chắc ! )

Không phải lời giải đâu

\(\frac{8}{14}+\frac{5}{12}+\frac{6}{14}+\frac{8}{12}-\frac{1}{12}\)

\(=\left(\frac{8}{14}+\frac{6}{14}\right)+\left(\frac{5}{12}+\frac{8}{12}-\frac{1}{12}\right)\)

\(=1+1=2\)

\(\frac{8}{14}+\frac{5}{12}+\frac{6}{14}+\frac{8}{12}-\frac{1}{12}\)

\(=\left(\frac{8}{14}+\frac{6}{14}\right)+\left(\frac{5}{12}+\frac{8}{12}-\frac{1}{12}\right)\)

\(=1+1=2\)

~ Hok tốt ~

\(4\cdot5\cdot\frac{6}{12}\cdot10\cdot8=\left(4\cdot5\right)\cdot\left(\frac{6}{12}\cdot8\right)\cdot10\)

\(=20\cdot4\cdot10=800\)

\(\frac{4\times5\times6}{12\times10\times8}=\frac{4\times5\times6}{2\times6\times5\times2\times2\times4}=\frac{1}{2\times2\times2}=\frac{1}{8}\)

\(\frac{4x5x6}{12x10x8}\)=\(\frac{1x1x1}{2x2x2}\)= \(\frac{1}{8}\)

dap an= 1/6 nha ban

\((\frac{1}{2}+\frac{1}{4}+\frac{1}{6}) \)x \((\frac{36}{9}-\frac{12}{9}:\frac{1}{3}) \)

\(= (\frac{1}{2}+\frac{1}{4}+\frac{1}{6}) \) x \((\frac{36}{9}-\frac{36}{9})\)

\( = (\frac{1}{2}+\frac{1}{4}+\frac{1}{6}) \) x \(0\)

\(= 0\)

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 

= ( 1 + 12 ) + ( 2 + 11 ) + ( 3 + 10 ) + ( 4 + 9 ) + ( 5 + 8 ) + ( 6 + 7 ) 

=     13         +     13       +     13       +      13     +    13      + 13

=               13 x 6 

=                 78

sai thui

1+2+3+4+5+6+7+8+9+10+11+12

=(1+9)+(2+8)+(3+7)+(4+6)+(5+10)+(11+12)

=10+10+10+10+15+23

=10×4+15+23

=40+15+23

=55+23

=78

ủng hộ nha có gì sai sót mong bạn thông cảm cho !!!

A  =\(\frac{2}{5}\times\frac{4}{7}+\frac{3}{5}\times\frac{4}{7}\)  B = \(\frac{17}{13}\times\frac{12}{17}-\frac{4}{13}\times\frac{12}{17}\)   C = \(\frac{9}{14}:\frac{6}{7}+\frac{5}{14}:\frac{6}{7}\)  D =\(\frac{9}{12}:\frac{7}{9}\times\frac{12}{19}\)

=  \(\frac{4}{7}\times\left(\frac{2}{5}+\frac{3}{5}\right)\)              =\(\left(\frac{17}{13}-\frac{4}{13}\right)\times\frac{12}{17}\)                = \((\frac{9}{14}+\frac{5}{14}):\frac{6}{7}\)         = \(\frac{9}{12}\times\frac{9}{7}\times\frac{12}{19}\)

=\(\frac{4}{7}\times1\)                                     = \(1\times\frac{12}{17}\)                                       = \(1:\frac{6}{7}\)                               = \(\frac{9\times9\times12}{12\times7\times19}\)

=\(\frac{4}{7}\)                                              =  \(\frac{12}{17}\)                                                =\(\frac{7}{6}\)                                    = \(\frac{9\times9}{7\times19}=\frac{81}{133}\)

   -  

mk tưởng bn học lớp 1

kg có cậu trả lời đi

\(\dfrac{3}{12}\)x\(\dfrac{15}{6}\)x\(\dfrac{8}{5}\)

=> \(\dfrac{5}{8}\)x\(\dfrac{8}{5}\)

=>1

\(\dfrac{3}{12}\times\dfrac{15}{6}\times\dfrac{8}{5}=1\)