Răspuns :

a-primul clasor
b-al dpoilea clasor
a+b=1000
b=3/7·a inlocuim
a+3a/7=1000 aducem la acelasi numitor
10a/7=1000
10a=7·1000
a=7000/10
a=700
b=1000-700=300
sau b=3·700/7=300
in I clasor 700 timbre
II clasor 300 timbre
a+b=1000;
b=3a/7 ⇒ a+3a/7=1000 ⇒7a+3a=7000 ⇒ a=700, b=300