There are three red and three blue balls in a bag. A ball is drawn from the bag. Without keeping the first ball back in the bag, a second ball is drawn from the bag. The probability of both balls being of different colours is :
One medicine of fever helps $75 \%$ of the patients. If three persons who are suffering from fever use this medicine, the probability of all the three persons getting benefitted from the medicine is :
The probability of a teacher taking test in class is $\frac{1}{3}$. If a student is absent twice, then his probability of at least not giving one test is :