Probability

From the Washington State 1996 Math Olympiad

1). (2 points) Of all the families that have only two children,
what is the probability that at least one is a girl?




Answer:__________

TEAM NO ____ TEAM MEMBERS:

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2). (3 points) A bag contains red, white and blue marbles.
The probability of drawing a red marble is 1/3
and the probability of drawing a white marble is 1/5.
What is the probability of drawing a blue marble?


Answer:__________

3). (3 points) A bag contains 2 yellow marbles,
4 blue marbles and 6 red marbles.
How many blue marbles must be added to the bag
to make the probability of drawing a blue marble 1/2 or 50%?


Answer:__________

4). (3 points) In a game you flip 3 chips.
Chip #1's sides are blue and red;
#2's are blue and white;
and #3 has red and white.
The first player gets a point if any 2 chips match.
To be fair, how many points should the second player
get if all 3 chips are different?

Answer:__________


5). (3 points) A bag has 10 candies. We drew a candy out, looked at it,
and put it back 10 times, and we noticed we got 4 fireballs.
We repeated the experiment four times and got 2, 5, 4, and 2 fireballs.
How many fireballs are most likely to be in the bag?

Answer:__________