a] 1/2 x 1/3 + 1/3 x 1/5= 1/3 x [ 1/2 + 1/5 ] = 1/3 x 7/10 = 7/30
1/2 x  1/3 + 1/3 x 1/5 = 1/6 + 1/15= 5/30 + 2/ 30 = 7/30
b] [ 2/5 + 3/10 ] x 1/2 = [4/10 + 3/10] x 1/2 = 7/10 x 1/2 = 7/20
( 2/5 +3/10)x 1/2= 2/5 x 1/2 + 3/10 x 1/2= 1/5 + 3/20= 7/20
c, ( 5/3 - 1/4 ) : 1/3 =  ( 20/12 - 3/12 ) : 1/3 = 17/12 : 1/3 = 17/12 x 3/1 =51/12
( 5/3 -1/4 ) : 1/3= 5/3 : 1/3 - 1/4 : 1/3= 5/3 x 3/1 - 1/4 x 3/1= 15/3 - 3/4 = 60/12- 9/12 =51/12= 17/4
d, 5/7 x 2/3 - 2/3 x 1/5 = 10/21 - 2/15= 150/315 - 42/315= 12/35
5/7 x 2/3 - 2/3 x 1/5 = 2/3 x ( 5/7 - 1/5 ) = 2/3 x ( 25/35 - 7/35 )= 2/3 x 18/35 = 36/105= 12/35