Răspuns:
a) 728•89+11•729=
729•89+(728+1)•11
729•89+729•11
729(89+11)
729•100
72900
b) 319+317•999=
319•999+(317+2)
319•999+319•1
319(999+1)
319•1000
319.000
c) 806•101-806•1
806(101-1)
806•100
80.600
d) 3+6+9+…+51
=3•1+3•2+3•3+…+3•17
=3(1+2+3+…+17)
=17•16:2
=17•8
=136