Hey there,
First, find the square root of the given equation.
Keep in mind that this is solved for k = 0 and 1.
Second, simplify.

Best of Luck!
Since a fraction is a form of division, you do 21/2=10 and 1/2.
Answer:

Step-by-step explanation:
This is a conditional probability exercise.
Let's name the events :
I : ''A person is infected''
NI : ''A person is not infected''
PT : ''The test is positive''
NT : ''The test is negative''
The conditional probability equation is :
Given two events A and B :
P(A/B) = P(A ∩ B) / P(B)

P(A/B) is the probability of the event A given that the event B happened
P(A ∩ B) is the probability of the event (A ∩ B)
(A ∩ B) is the event where A and B happened at the same time
In the exercise :



We are looking for P(I/PT) :
P(I/PT)=P(I∩ PT)/ P(PT)

P(PT/I)=P(PT∩ I)/P(I)
0.904=P(PT∩ I)/0.025
P(PT∩ I)=0.904 x 0.025
P(PT∩ I) = 0.0226
P(PT/NI)=0.041
P(PT/NI)=P(PT∩ NI)/P(NI)
0.041=P(PT∩ NI)/0.975
P(PT∩ NI) = 0.041 x 0.975
P(PT∩ NI) = 0.039975
P(PT) = P(PT∩ I)+P(PT∩ NI)
P(PT)= 0.0226 + 0.039975
P(PT) = 0.062575
P(I/PT) = P(PT∩I)/P(PT)

3 feet 8 inches converted to inches is 3x12+8=44inches
44inches times 4 pieces is 176 inches.
176 inches converted back to feet and inches is 176/12=14 feet 8 inches so he would need 15 feet of board