I have a probability question I cannot do, plz help!?

Question

Question 4
The prob. of stock A rising is 0.3; and of
stock B rising is 0.4. What is the prob.
that neither of the stocks rise, assuming
that these two stocks are independent?
1. 0.42
2. 0.12
3. 0.88
4. 0.44
Question 5
If the above stocks are not independent,
and the prob. of both stocks rising is 0.09,
what is the prob. that neither stock rises?
1. 0.69
2. 0.39
3. 0.42
4. 0.52

Answer 1

P(A) = 3/10 P(A)' = 7/10
P(B) = 4/10 P(B)' = 6/10

P(AUB)' = P(A)'xP(B)'
7/10x6/10 = 42/10
= .42

if above stocks are not independent
P(A intersection B) = 9/100
P(AUB) = P(A)+P(B) - P(A intersection B)
P(AUB) = 3/10+4/10 - 9/100
P(AUB) = 61/100
P(AUB)' = 1-P(AUB)
1-61/100
39/100
.39

Answer 2

if they are independent, you multiply the probabilities
if they are dependent, you add (or subtract) the probabilities

(1 - 0.3) * (1 - 0.4) = 0.7*0.6 = 0.42
1 - (0.3 + 0.4 - 0.09) = 1 - (0.61) = 0.39

note: if the probability of an event happening is A, the probability that it doesn't happen is 1 - A

Answer 3

4. (1 - 0.3)(1 - 0.4) = 0.7*0.6 = 0.42
5. 1 - (0.3 + 0.4 - 0.09) = 1 - (0.61) = 0.39

Answer 4

4) 1 - (0.4+0.3 -0.4*0.3) = 1-0.58 = 0.42

5) 1-(0.4+0.3-0.09) = 0.39