3×a - a:3 = 800 |×3
9×a - a = 2 400
8×a = 2 400
a = 2 400: 8
a = 300
Verificare:
3×300 - 300:3 = 900-100 = 800
Metoda grafica:
3×a |___|___|___|___|___|___|___|___|___|
a:3 |___|
avem 9 segmente egale - 1 segment egal = 8 segmente egale = 800
800 : 8 = 100 (un segment egal)
3×a = 9×100 = 900
a:3 = 100
a = 100×3
a = 300
