13.Calculati aducând la același numitor :
d). 11/25-7/100+1/5-3/20
e).5/9+7/6+9/4+6/36
f).7/150+11/50+1/300+23/100


14.Calculati :
a). 1/23 + 2/23 + 3/23 +... + 22/23
b). 1/21 + 2/21 + 3/21 +... +20/21.


15.Calculati folosind proprietățile adunării :
a). 11/45 + ( 5/8 + 31/41) + 34/45 + (3/8 + 10/41) ;
b). (6/9+35/48)+3/9+(17/39 + 13/48) +22/39.


Ajutorr, va rog! ​