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Topic: Re:Re:Re:That impossible 'maths' question...
Posted by: David Noades
Date/Time: 05/06/15 16:09:00

Try this:

The probability that the first sweet is orange is 6/n (6 out of n sweets are orange).

Given that the first sweet is orange, the probability of the second one being orange is 5/(n-1) (one orange sweet has gone and there is now one less sweet in the bag).

To get the probability of both events occurring we multiply the two, so:

P = 6/n x 5/(n-1).

But we are also told in the question that the probability of these two events occurring is 1/3, so:

1/3 = 6/n x 5/(n-1)

Which gives:

1/3 = 30/(n^2 -n)

30 = (n^2 - n)/3

n^2 - n = 90

and finally:

n^2 -n -90 = 0

Factoring this gives solutions of n=10 or n=-9 and since you can't have a negative number of sweets (well not in my world anyway!), the total original number of sweets in the bag must be 10, with 6 of these being orange and 4 being yellow.


Entire Thread
TopicDate PostedPosted By
That impossible 'maths' question...05/06/15 14:06:00 Anuj Gupta
   Re:That impossible 'maths' question...05/06/15 14:41:00 Janet Norman
   Re:That impossible 'maths' question...05/06/15 14:46:00 Andy Rooney
      Re:Re:That impossible 'maths' question...05/06/15 14:56:00 Andy Rooney
         Re:Re:Re:That impossible 'maths' question...05/06/15 15:09:00 Barry Jacques
            Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:13:00 Andy Rooney
               Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:16:00 bobby osborne
                  Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:20:00 Andy Rooney
                  Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:28:00 Barry Jacques
               Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:21:00 Barry Jacques
                  Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:41:00 Andy Rooney
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 15:57:00 Barry Jacques
   Re:That impossible 'maths' question...05/06/15 14:58:00 Barry Jacques
      Re:Re:That impossible 'maths' question...05/06/15 15:51:00 Will Watson
         Re:Re:Re:That impossible 'maths' question...05/06/15 16:04:00 Andy Rooney
            Re:Re:Re:Re:That impossible 'maths' question...05/06/15 16:06:00 Barry Jacques
         Re:Re:Re:That impossible 'maths' question...05/06/15 16:04:00 Barry Jacques
            Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:53:00 Jim Meddings
               Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 18:32:00 Barry Jacques
         Re:Re:Re:That impossible 'maths' question...05/06/15 16:09:00 David Noades
            Re:Re:Re:Re:That impossible 'maths' question...05/06/15 16:15:00 Will Watson
            Re:Re:Re:Re:That impossible 'maths' question...05/06/15 16:21:00 Barry Jacques
               Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 16:44:00 David Noades
               Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 16:48:00 Anuj Gupta
                  Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 16:51:00 Vanessa Smith
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:00:00 Micki Hawkes
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...06/06/15 12:57:00 Vanessa Smith
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 18:58:00 Barry Jacques
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...06/06/15 12:10:00 Peter Evans
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...06/06/15 13:01:00 Vanessa Smith
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...06/06/15 12:26:00 Will Watson
                  Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:10:00 Andy Rooney
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:22:00 Andy Pease
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:27:00 Andy Rooney
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:30:00 Anuj Gupta
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 17:37:00 Adrian Irving
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 18:49:00 Barry Jacques
                           Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 19:09:00 bobby osborne
                           Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 20:08:00 Anne England
                              Re:Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...05/06/15 22:57:00 Al Webber
                                 Re:Re:Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...06/06/15 09:46:00 David Turner
                     Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 09:29:00 Anuj Gupta
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 09:39:00 Will Watson
                           Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 12:01:00 Brian Coyle
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 12:05:00 Barry Jacques
                           Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 14:03:00 Anne England
                           Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 15:43:00 Anuj Gupta
                              Re:Re:Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 15:52:00 Peter Evans
                        Re:Re:Re:Re:Re:Re:Re:Re:That impossible 'maths' question...08/06/15 12:14:00 Barry Jacques

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