Notam astfel:
a = zilele petrecute la bunici
b = zilele petrecute acasa
c = zilele petrecute cu familia in excursie
a + b + c = 72 zile
a = b - 7 ==> b = a + 7 = 2×c + 7
a = 2×c
inlocuim in prima relatie in functie de c
2×c + 2×c + 7 + c = 72
5×c = 72 - 7
5×c = 65
c = 65:5
c = 13 zile (cu familia)
a = 2×13 = 26 zile (la bunici)
b = 2×13+7 = 26+7 = 33 zile (acasa)
verificare:
26 + 33 + 13 = 72 zile (in total)
metoda grafica:
a /----/----/
b /----/----/+7
c /----/
5 segmente egale +7 = 72
72 - 7 = 65
65 :5 = 13 (un segment egal)
a = 2×13 = 26
b = 2×13 + 7 = 33
c = 13
