a+b+c=3000
a*(100%-75%)=b*(100%-80%)=c*(1-2/3)
a*1/4=b*1/5=c*1/3
a*1/4=b*1/5
a=b*4/5
b*1/5=c*1/3
c=b*3/5
4/5*b+b+3/5*b = 3000
12b=15000
b=1250 pag.
a=4/5*b=1000 pag.
c=3/5*b=750 pag.
timp necesar citirii vol3 = x * timp necesar citirii vol2
750= x * 1250
x =750/1250 = 0.6
x= 60%