9. Dacă a<b, atunci a:c<b:c
Dacă a:c<b:c,atunci a<b
(a+b):c=a:c+b:c
(a-b):c=a:c-b:c
(a×b):c=a×(b:c)=b×(a:c)
a:(b×c)=(a×b):c=(a×c):b
12. a) 360-64-26=
=296-26=270
b) 360-(74+26)=
=360-100=260
11. a) 22+44+66+88=
=22(1+2+3+4)=
=22×10=220
b) 11+33+55+77+99=
=11(1+3+5+7+9)=
=11[(1+2+3+...+9)-(2+4+6+8)]=
=11[(9×10)/2-20]=
=11(9×5-20)=
=11(45-20)=
=11×25=275
