11. Jumatate la sah, deci 1/2=6/12 din elevi
iar 7/12 la filatelie, deci cu cel putin 1 mai mult decat 1/2=6/12, pt ca 7/12 > 6/12=1/2
12. Maimute in total = x
5x/7(7/7-2/7 = fara cele care se catara in copaci) * 3/5 = 3x/7 fac tumbe
x-(2x/7 + 3x/7) = 4
x-5x/7 = 4
2x/7 = 4 I :2
x/7=2
x=14