Fie a, b,c,d, nr de paini cumparate de cei 4 cumparatori si p numarul total de paini existente.
a+b+c+d=p
a=p/2+1/2
dupa ce a cumparat a, a ramas r=p-p/2-1/2=(p-1)/2
b=r/2+1/2
dupa ce a cumparat b, a ramas s=r-r/2-1/2=(r-1)/2
c=s/2+1/2
dupa ce a cumparat c, a ramas t=s-s/2-1/2=(s-1)/2
d=t/2+1/2
dupa ce a cumparat d, a ramas u=t-t/2-1/2=(t-1)/2=0 pentru ca la sfarsit nu a mai ramas nicio paine
=> (t-1)/2=0=> t-1=0=> t=1
dar stim ca t=(s-1)/2
=> (s-1)/2=1=>
=> s-1=2=>
=> s=3
dar stim ca s=(r-1)/2
=> (r-1)/2=3=>
=> r-1=6=>
=> r=7
dar stim ca r=(p-1)/2
=> (p-1)/2=7
=> p-1=14
=> p=15
Deci, in total au fost 15 paini.
