from math import sqrt
def parametres():
    m=(2.5*3+2.7*5+2.8*8+3.1*7+3.4*5+3.5*3+3.9)/(3+5+8+7+5+3+1)
    v=(3*(2.5-m)**2+5*(2.7-m)**2+8*(2.8-m)**2+7*(3.1-m)**2
    +5*(3.4-m)**2+3*(3.5-m)**2+(3.9-m)**2)/(3+5+8+7+5+3+1)
    s=sqrt(v)
    return(m,s)

def intervalle():
    (m,s)=parametres()
    inf=m-2*s
    sup=m+2*s
    return(inf,sup)
    
def mystere():
    n=0
    (inf,sup)=intervalle()
    L=[2.5,2.5,2.5,2.7,2.7,2.7,2.7,2.7,2.8,2.8,2.8,2.8,2.8,2.8,2.8,
    2.8,3.1,3.1,3.1,3.1,3.1,3.1,3.1,3.4,3.4,3.4,3.4,3.4,
    3.5,3.5,3.5,3.9]
    for i in L:
        if i>=inf and i<=sup:
            n=n+1
    p=n/32
    return(p)