a) c1 

( 1/3 - 1/5 ) x 1/2 = 2/15 x 1/2 = 1/15

c2 

( 1/3 - 1/5 ) x 1/2= 1/3 x 1/2  - 1/5 x 1/2 

= 1/6 - 1/10 = 1/15 

b ) c1 

( 1/3 + 1/5 ) x 1/2 =  8/15 x 1/2 = 4/15 

c2 

(1/3 + 1/5 ) x 1/2 = 1/3 x 1/2 + 1/5 x 1/2

= 1/6 + 1/10 = 4/15 

chúc bn học tốt   

$(\dfrac{1}{3}-\dfrac{1}{5})×\dfrac{1}{2}$

$C1:$

$=(\dfrac{5}{15}-\dfrac{3}{15})×\dfrac{1}{2}$

$=\dfrac{2}{15}×\dfrac{1}{2}$

$=\dfrac{\not2.1}{15.\not2}$

$=\dfrac{1}{15}$

$C2:$

$=\dfrac{1}{3}×\dfrac{1}{2}-\dfrac{1}{5}×\dfrac{1}{2}$

$=\dfrac{1.1}{3.2}-\dfrac{1.1}{5.2}$

$=\dfrac{1}{6}-\dfrac{1}{10}$

$=\dfrac{5}{30}-\dfrac{3}{30}$

$=\dfrac{2}{30}$

$=\dfrac{1}{15}$

$(\dfrac{1}{3}+\dfrac{1}{5})×\dfrac{1}{2}$

$C1:$

$=(\dfrac{5}{15}+\dfrac{3}{15})×\dfrac{1}{2}$

$=\dfrac{8}{15}×\dfrac{1}{2}$

$=\dfrac{\not84.1}{15.\not2}$

$=\dfrac{4}{15}$

$C2:$

$=\dfrac{1}{3}×\dfrac{1}{2}+\dfrac{1}{5}×\dfrac{1}{2}$

$=\dfrac{1.1}{3.2}+\dfrac{1.1}{5.2}$

$=\dfrac{1}{6}+\dfrac{1}{10}$

$=\dfrac{5}{30}+\dfrac{3}{30}$

$=\dfrac{8}{30}$

$=\dfrac{4}{15}$