s-suprafata totala
100=5/12·s
s=100:5/12
s=100·12/5
s=240 ha
notam a, b - suprafata arata in a doua si in a treia zi
a=3/2·b
a+b=240-100
3/2·b+b=140 |·2
3b+2b=280
5b=280
b=56
a=3/2·56=3·28=84
verificare: 84+56=140
100=5/12 ·240
Deci: in a doua zi s-au arat 84ha iar in a treia zi 56ha.