Answer:
a) 
b) 
And replacing we got:

c) 


And adding we got:

Step-by-step explanation:
Previous concepts
The binomial distribution is a "DISCRETE probability distribution that summarizes the probability that a value will take one of two independent values under a given set of parameters. The assumptions for the binomial distribution are that there is only one outcome for each trial, each trial has the same probability of success, and each trial is mutually exclusive, or independent of each other".
Solution to the problem
Let X the random variable of interest, on this case we now that:
The probability mass function for the Binomial distribution is given as:
Where (nCx) means combinatory and it's given by this formula:
Assuming the following questions:
a. exactly five
For this case we can use the probability mass function and we got:

b. at least one
For this case we want this probability:

And we can use the complement rule and we got:


And replacing we got:

c. between four and six, inclusive.
For this case we want this probability:




And adding we got:

31,
because when you divide 42 and 12 to get the other two sides you get 3.5 and
3.5+3.5+12+12=31
The answer is 1 please give brainliest answer! If you do I’ll show you the most amazing app ever
Answer:
68
Step-by-step explanation:
Let:
Number of girls invited = x
Number of boys = x +20
3/4 of boy showed up
2/3 of girls showed up
Exactly 19 did not show up
Therefore, we could say:
Fraction of boys that didn't show up = 1 - 3/4 = 1/4
Fraction of girls that didn't show up = 1 - 2/3 = 1/3
That is,
[1/4 *(x + 20)] + [1/3*x] = 19
[(x + 20) / 4] + x /3 = 19
(3(x + 20) + 4x) / 12 = 19
3x + 60 + 4x = 228
7x = 228 - 60
7x = 168
x = 168 / 7
x = 24
Number of girls, x = 24
Number of boys, x + 20 = 24 + 20 = 44
Total friends invited = (24 + 44) = 68