Răspuns:
5/6+2/9=(3×5+2×2)/18=(15+4)/18=19/18
5/6-2/9=15-4)/18=11/18
13/6+b=3,,b=3-13/6=(18-13)/6=5/6
13/6-5/6=(13-5)/6=8/6=4/3
7/8-b=1/2 ,-b=1/2-7/8=(4-7)/8=(-3/8) b=3/8
7/8+3/8=10/8=5/4
7/8-3/8=4/8=1/2
a+3/10=2 a=2-3/10=(20-3)/10=17/10
17/10-3/10=14/10=7/5
a-13/12=2/3 a=2/3+13/12=(4×2+13)/12=(8+13)/12=21/12=7/4
7/4+13/12=3×7+13)/12=(21+13)/12=34/12=17/6
