A teacher selects a student at random from his class of 20 students every week for 20 consecutive weeks. There are 8 girls and 12 boys in the class. What is the probability that there are exactly 12 weeks in which a girl is selected

The value is  

Step-by-step explanation:

From the question we are told that

   The number of boys in the class is  

   The number of girls in the class is  

   The total number of students is  is  n  =  20

    The number of weeks is  N  = 20

The probability of selecting a girl is mathematically represented as

=>

The probability of not  selecting a girl is mathematically represented as  

=>

Generally the selection of students from the class  follows a binomial distribution  

i.e  

and the probability distribution function for binomial  distribution is  

Here C stands for combination hence we are going to be making use of the combination function in our calculators  

Generally the probability that there are exactly 12 weeks in which a girl is selected is mathematically represented as

=>  

75 tickets have been sold so far.

step-by-step explanation:

in this question it is clearly mentioned that 45 children's tickets have been sold and this number is 60% of the total tickets sold.

now let's assume the total number of tickets sold be x.

then 60% of x = 45

⇒

⇒ x(.6) = 45

by dividing with .6 on both the sides of the equation

⇒ x = 75

therefore 75 tickets have been sold so far.

associative property hopes this ! : )

step-by-step explanation: