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Topic: Re:Re:Re:That impossible 'maths' question...
Posted by: Barry Jacques
Date/Time: 05/06/15 16:04:00

If Hannah takes a sweet from the bag on her first selection, there is a 6/n chance it will be orange.

That’s because there are 6 oranges and n sweets.

If Hannah takes a sweet from the bag on her second selection, there is a 5/(n-1) chance it will be orange.

That’s because there are only 5 orange sweets left out of a total of n - 1 sweets.

The chance of getting two orange sweets in a row is the first probability MULTIPLIED BY the second one. (Separate lesson 😊)

Which is 6/n x 5/n–1

The question tells us that the chance of Hannah getting two orange sweets is 1/3.

So: 6/n x 5/n–1 = 1/3

Rearranging this equation

(6x5)/n(n-1) = 30/(n2 – n) = 1/3

Or 90/(n2 – n) = 1

So (n2 – n) = 90

And, finally n2 – n – 90 = 0


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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