# Thread: Probability HELP!!!

1. ## Probability HELP!!!

How do I solve the following?

1) One card is drawn from a standard deck of cards.What is the Probabilty of drawing a black card or a seven?

2) A spinner with even sections numbered 1 through 5 is spun. What is the probabilty that the spinner will stop on a 2 or a 4?

HELP!!!

2. Originally Posted by lynncody
How do I solve the following?

1) One card is drawn from a standard deck of cards.What is the Probabilty of drawing a black card or a seven?
i assume we are dealing with a 52-card deck that has no jokers. There are 52 cards in all, half of them are black, and 4 of them are 7's

so there are 26 possible black cards we can draw from the deck of 52, and 4 7's we can draw out of the deck of 52

when we want to find the probability of one event OR another event happening, we add their respective probabilities.

thus, the probability of drawing a black card or a 7 is: $\frac {26}{52} + \frac {4}{52}$ ...i leave simplifying that to you

EDIT: i forgot to account for repeats. that is, what if the black card is a 7? see Plato's solution on how to deal with this

3. Originally Posted by lynncody
2) A spinner with even sections numbered 1 through 5 is spun. What is the probabilty that the spinner will stop on a 2 or a 4?

HELP!!!
since one of the five sections is marked with a 2, the probability of the spinner stoping on a 2 is 1/5. similarly, the probability of stoping on a 4 is 1/5

what is the probability of stopping on a 2 OR 4 (see my last post)

4. 1) One card is drawn from a standard deck of cards.
What is the Probabilty of drawing a black card or a seven?
$\begin{array}{rcl}
P(B \cup S) & = & P(B) + P(S) - P(B \cap S) \\
& = & \frac{1}{2} + \frac{1}{{13}} - \frac{2}{52} \\
\end{array}$

2) A spinner with even sections numbered 1 through 5 is spun. What is the probabilty that the spinner will stop on a 2 or a 4?
$\frac{2}{5}$???