Răspuns :
[tex] \frac{1}{4} + \frac{5}{7} = \frac{7}{28} + \frac{20}{28} = \frac{27}{28} [/tex]
Aflam c.m.m.m.c. care este 28
7)1 7
----= ------
4 28
4)5 20
----= -----
7 28
7 20 27
---+ ---= ---
28 28 28
7)1 7
----= ------
4 28
4)5 20
----= -----
7 28
7 20 27
---+ ---= ---
28 28 28