The probability of getting two heads when three balanced coins are tossed is ............

In a medical examination of students of a class,the following blood groups are recorded:

Blood group	$A, AB, B, O$
Number of students	$10, 13, 12, 5$

$A$ student is selected at random from the class. The probability that he/she has blood group $B$,is:

$80$ bulbs are selected at random from a lot and their lifetime (in $hrs$) is recorded in the form of a frequency table given below:

Lifetime (in hours)	$300$	$500$	$700$	$900$	$1100$
Frequency	$10$	$12$	$23$	$25$	$10$

One bulb is selected at random from the lot. The probability that its lifetime is $1150$ hours is:

The maximum value of the probability of any event is ...........

On tossing two coins simultaneously,find the probability of getting no tail.

Can the experimental probability of an event be a negative number? If not,why?