Răspuns :
a) pai exista 3 moduri :
(3×5)×2=30
(3×2)×5=30
(2×5)×3=30
b) (7×3)×2=42
(7×2)×3=42
(2×3)×7=42
c) (2×9)×4=72
(4×9)×2=72
(4×2)×9= 72
(3×5)×2=30
(3×2)×5=30
(2×5)×3=30
b) (7×3)×2=42
(7×2)×3=42
(2×3)×7=42
c) (2×9)×4=72
(4×9)×2=72
(4×2)×9= 72