Suppose you are taking a 15 question True/False quiz which you are not prepared for. You find yourself simply guessing at every answer. What is the probability that you get less than 3 answers correct?

And adding the results we got:

Step-by-step explanation:

We can define the variable of interest s X representing the number of correct questions for the exam. and we can model this random variable with a binomial distribution. The probability of select the correct answer would be since is a true/false question.

And we want to find this probability:

The probability mass function for the Binomial distribution is given as:

Where (nCx) means combinatory and it's given by this formula:

And we want to find this probability:

We can find the individual probabilities and we got:

And adding the results we got:

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18