Răspuns:
a) 26×2+31= 52+31= 83 cm
b) 16×4= 64 cm
c) 399×2= 798
(399+406)×2= 805×2= 1610
798+ 1610= 2408 cm
d) 2×(3×108)= 648
2×108+ 2×648= 216+ 1296= 1512 cm
