21/11 × 22/17 × 68/63

= (21 × 2 × 4)/63

= 8/3

a)8/3

b,1/5 tk cho mk nha pn

b; \(\dfrac{5}{14}\) \(\times\) \(\dfrac{7}{13}\) x \(\dfrac{26}{25}\)

= \(\dfrac{5\times7\times2\times13}{7\times2\times13\times5\times5}\)

= \(\dfrac{5\times7\times2\times13}{5\times7\times2\times13}\) x \(\dfrac{1}{5}\)

= 1 x \(\dfrac{1}{5}\)

= \(\dfrac{1}{5}\)

a; \(\dfrac{21}{11}\) x \(\dfrac{22}{17}\) x \(\dfrac{68}{63}\)

= \(\dfrac{21\times11\times2\times17\times4}{11\times17\times21\times3}\)

= \(\dfrac{11\times17\times21}{11\times17\times21}\) x \(\dfrac{2\times4}{3}\)

= 1 x \(\dfrac{8}{3}\)

= \(\dfrac{8}{3}\)

\(\frac{21}{11}\)x \(\frac{22}{17}\)x\(\frac{68}{63}\)

= \(\frac{42}{17}\)x\(\frac{68}{63}\)

= \(\frac{8}{3}\)

18 - x : 2 = 16

x : 2        = 18 - 16

x             = 2 x 2

x             = 4

\(\frac{21}{11}\times\frac{22}{17}\times\frac{68}{63}\)

\(=\frac{21}{11}\times\frac{22\times68}{17\times63}\)

\(=\frac{21}{11}\times\frac{22\times4}{1\times63}\)

\(=\frac{21}{11}\times\frac{88}{63}\)

\(=\frac{21\times88}{11\times63}\)

\(=\frac{1\times8}{1\times3}\)

\(=\frac{8}{3}\)

\(18-x:2=16\)

\(x:2=18-16\)

\(x:2=2\)

\(x=2\times2\)

\(x=4\)

Tính theo cách thuận tiện : 

21/11 × 22/17 × 68/63

= ( 21/11 × 68/63 ) × 22/17

= 68/33 × 22 / 17

= 8/3

Tìm x , biết : 

18-x:2=16

x:2=18-16

x:2=2

x=2×2

= 4

Vậy x = 4

21/11 x 22/17 x 68/63 = 952/357

5/14 x 7/13 x 6/25=3/65

\(\frac{21}{11}X\frac{22}{17}X\frac{68}{63}=\frac{952}{357} \)

\(\frac{5}{14}X\frac{7}{13}X\frac{6}{25}=\frac{3}{65}\)

ko iểu

21/11 x 22/17x68/63

= 7x3x2x11x4x17      /           11x17x7x3x3

=8/3

5/14x7/13x26/25

=5x7x26              /                14x13x25

= 5x7x13x2             /              7x2x13x5x5

=1/5

cậu có thể giảng kĩ hơn được ko mình ko hiểu 1 tí nào 

a; \(\dfrac{21}{11}\) x \(\dfrac{22}{17}\) x \(\dfrac{68}{63}\)

= \(\dfrac{21\times11\times2\times17\times4}{11\times17\times21\times3}\)

= \(\dfrac{11\times17\times21}{11\times17\times21}\) x \(\dfrac{2\times4}{3}\)

= 1 x \(\dfrac{8}{3}\)

= \(\dfrac{8}{3}\)

b; \(\dfrac{5}{14}\) \(\times\) \(\dfrac{7}{13}\) x \(\dfrac{26}{25}\)

= \(\dfrac{5\times7\times2\times13}{7\times2\times13\times5\times5}\)

= \(\dfrac{5\times7\times2\times13}{5\times7\times2\times13}\) x \(\dfrac{1}{5}\)

= 1 x \(\dfrac{1}{5}\)

= \(\dfrac{1}{5}\)

cái này là 2 phép tính riêng biệt hay là gì hả bạn ?

2 phép tính khác nhau!

21/11 x 22/17x68/63 = 7 x 3 x 2 x 11 x 4 x 17 / 11 x 17 x 7 x 3 x 3 = 8 / 3

a)8/3

b)1/5