Ответ: N=N02^-t/T  0,75N0=N02^-t/T 0,75=2^-t/T 2^(1,2/T)=1,33Ln2^(1,2/T)=Ln1,33(1,2/Т)Ln2=Ln1,33Т=1,2Ln2/Ln1,33=2,9 c.