6th Test - Probabilities

Analysis of results

1) If the probability of rolling a 3 on a six sided dice is 1/6, what is the probability of rolling a 3 on an 8 sided dice? _______1/8_______

2) There are 52 cards in a deck of cards. If you pick a card at random, what is the probability of drawing an ace? ____1/13_____

there are 4 aces in an ordinary deck, so 4/52 can reduce to 1/13. I accepted 4/52 though.

3) In a jar there are 90 red jelly beans and 10 blue ones. If you pick a bean from the jar with your eyes closed what are the odds that you pick a blue one?_______1/10________

   10/(90 + 10) = 1/10

4) If the chance of rolling snake eyes (two ones) with a pair of dice is 1/36, what are the odds of the two dice summing to three (in other words rolling a 3)?   _______1/18________

   There are 2 ways to roll 3: 1 and 2 or a 2 and 1. So 2/36 = 1/18

5) If I throw 3 pennies, what is the probability that I get 2 tails and 1 head? ___3/8___

   There are 3 ways to get 2 tails and 1 head: TTH, THT, or HTT, and there are 8 total ways to roll/

6) A jar has only red and black marbles in it. I know that there are 1000 red marbles in the jar. If I reach in and grab a large handful of marbles and find that I selected 18 red marbles and 9 black marbles, how many black marbles should I guess are in the jar? ___500_______

    Set up a proportion like we have talked about   1000/x = 18/9, so x = 500

7) In my sock drawer I have 6 red socks, 8 blue socks, and 4 green socks. If I pull out socks one at a time, what is the greatest number of times that I might have to select a sock before I get a pair? (I do not replace a sock once it has been selected)   ___4 times______

   There are only 3 colors of sock, so on the 4th draw, we are guaranteed to get a match if not before.

8) If I roll 3 dice, how many different ways could I roll so that the dice sum to 4? __3___

There are three ways : 2,1,1 or 1,2,1 or 1,1,2. Order is important because it might have been just one die that you throw 3 times.

9) If I roll a 6 sided die, what is the probability of rolling a 7? ____0_____

You cannot do it. There is no 7 on a regular 6 sided die.

10) If you roll 2 dice what is the probability that the difference between the numbers on the 2 dice will be 5? ____1/18_____

there are only 2 ways to roll such that the difference is 5: 1 and 6, or 6 and 1.
So 2/36 = 1/18