Subject: check

secondary worksheet

I was wondering if you could let me know if I did these problems correctly, and if not can you let me know how to fix them, thanks Dee.

A card is selected from an ordinary deck of cards. What is the probability of. . . selecting 2 aces in a row?

i got .036038961

and

If you toss two dice, what would be your probability of the following?

  1. a sum of six - I got 5/36
     
  2. a sum of 9 or greater - I got 7/36
     
  3. a sum of four 3 times in a row - I got 1/729
     
  4. an even sum - I got 9/36

thanks

Hi Dee,

The answer to the first question depends on how you draw the two cards.

If you are selecting one card from a standard deck the probability of it being an ace is 4/52 = 1/13. If you got an ace and then select a second card the probability that it is an ace is 3/51. (There are only 51 cards left and only 3 aces.) Thus the probability that both are aces is 1/13 x 3/51.

If you are to put the first ace back in the deck before you draw the second card then the probability that the second card is an ace is also 4/52. In this case the probability of two aces is (4/52)2.

For the dice problem you should make a 6 by 6 chart of all the 36 possibilities of the result of tossing two dice, think of them as Red and Green.

	  1      2      3      4     5      6
1	(1,1)  (1,2)  (1,3)  (1,4) (1,5)  (1,6)
2	(2,1)  (2,2)  (2,3)  (2,4) (2,5)  (2,6)
3	(3,1)  (3,2)  (3,3)  (3,4) (3,5)  (3,6)
.         .      .      .      .     .      .
.         .      .      .      .     .      .

Looking at the table above I also got 5/36 for the first part. You can get a sum of six from (5,1), (4,2) (3,3), (2,4) and (1,5).

Now can you do the rest?

Penny
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