9/5 : 17/15 + 8/5 : 17/15

= 27/17 + 24/17

= 3

cách 2 

( 9/5 + 8/5 ) : 17/15

=17/5 : 17/15

= 3

0,9 : 0,25 + 1,05 : 0,25

= 3,6 + 4,2

= 7,8

cách 2

0,9 : 0,25 + 1,05 : 0,25

= ( 0,9 + 1,05 ) : 0,25

= 1,95 : 0,25

= 7,8

cách 1: 9/5:17/15 + 8/5:17/15=27/17+24/17=3

cách 2 :9/5:17/15+8/5:17/15=17/15 x15/17+8/5 x15/17=15/17 x (9/5+8/5)=15/17 x 17/5 = 3

a)

C1: 9/5 : 17/15 + 8/5 : 17/15

= 27/17 + 14/17

= 3

C2: 9/5 : 17/15 + 8/5 : 17/15

= ( 9/5 + 8/5 ) : 17/15

= 17/5 : 17/15

= 3

b)

C1: 0,9 : 0,25 + 1.05 : 0,25

= 3,6 + 4,2

= 7,8

C2: 0,9 : 0,25 + 1,05 : 0,25

= ( 0,9 + 1,05) : 0,25

= 1,95 : 0,25

= 7,8

fggfggfgfg

^fgfgfgfg

Cách hai:

A; \(\dfrac{17}{19}\) x \(\dfrac{12}{15}\) x \(\dfrac{19}{17}\)

= \(\dfrac{68}{95}\) x \(\dfrac{19}{17}\)

= \(\dfrac{4}{5}\)

Cách 1:

A. \(\dfrac{17}{19}\) x \(\dfrac{12}{15}\) x \(\dfrac{19}{17}\)

= (\(\dfrac{17}{19}\) x \(\dfrac{19}{17}\)) x \(\dfrac{12}{15}\)

= \(1\) x \(\dfrac{12}{15}\)

= \(\dfrac{4}{5}\)

B; Cách 1: (\(\dfrac{5}{7}\) + \(\dfrac{9}{7}\)) x \(\dfrac{21}{28}\)

                 =  2 x \(\dfrac{3}{4}\)

                 =   \(\dfrac{3}{2}\)

Cách 2:   (\(\dfrac{5}{7}+\dfrac{9}{7}\)) x \(\dfrac{21}{28}\) 

             =  \(\dfrac{5}{7}\) x \(\dfrac{21}{28}\) + \(\dfrac{9}{7}\) x \(\dfrac{21}{28}\)

             =   \(\dfrac{15}{28}\) + \(\dfrac{27}{28}\)

            = \(\dfrac{42}{28}\)

            = \(\dfrac{3}{2}\)