Bonsoir,
a)1/3+2/3÷5/7
= 1/3 +2/3 * 7/5
= 1/3 +14 /15
= 5/15 + 14/15
= 19/15
b)5/4-3/2÷-2/5+1/4
= 4 - 3/2* 5/2 +1/4
= 4- 15/4 +1/4
= 16/4 -15/4 +1/4
= 2/4
= 1/2
c)-7/3×2/7÷-3/7×14/3
=-7/3 * 2/7 *7/3 *14/3
= - 1 372/3
d)-2÷5/12-3/4
= -2 *12/5 -3/4
= -24/5 -3/4
= -96/20 - 15/20
= -81/20
e)2-4/3÷-2
= 2- 4/3 * -1/2
= 2+4/6
= 12/6 +4/6
=20/6
= 10/3
f)9/2×(7/9-5/12)
9/2 *( 28/36 - 15/36)
= 9/2 * 13/36
= 117/72
=39/24
= 13/ 8