Notam cu [tex] s_{1} s_{2} s_{3} .......s_{12}[/tex] media inaltimii spiridusilor si cu[tex] z_{1} z_{2} z_{3}......... z_{n} [/tex] media inaltimii zanelor
[tex] \frac{ s_{1} + s_{2} +......+s_{12}}{12} [/tex] = 60 => suma inaltimii spiridusilor este 780
[tex] \frac{z_{1}+ z_{2}+ z_{3}+......... z_{n}}{n} [/tex] = 160 => suma inaltimii zanelor este 160n
[tex] \frac{780+160n}{12+n} [/tex]=120=>720+160n =120(n+12) => 720+160n = 1440+120n => 160n -120n = 1440 - 720 =>40n = 720 => n = 18
Deci sunt 18 zane
