It is currently Fri Jul 21, 2017 12:48 pm

 All times are UTC

 Page 1 of 1 [ 5 posts ]
 Print view Previous topic | Next topic
Author Message
 Post subject: digitsPosted: Sun Jun 08, 2008 3:40 pm

Joined: Fri Mar 07, 2008 9:27 am
Posts: 18
Hi

These are the four two-digit numbers that can be made with the digits 1and 7.

11 17 71 77

How many three-digit numbers can be made with the digits 1,2 and 3?.

(a) 6
(b) 9
(c) 21
(d) 27

Top

 Post subject: Posted: Sun Jun 08, 2008 3:43 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13016
27 I think

each time there are three numbers to chose from so 3 x 3 x 3

Top

 Post subject: Posted: Sun Jun 08, 2008 7:33 pm

Joined: Fri Mar 17, 2006 5:12 pm
Posts: 1328
Location: Birmingham
Hi Lala

27 is incorrect

The question is asking for the number of permutatons of 3 numbers taken three at a time.

There is a matherical formula which is: p = n!/ (n-r)!

Where n! means factorial = n x (n-1) x (n-2).....x 1

Hence for this p = 3 x2 x1 = 6

You can also work this ourt using the various sequences:-

Start with 1 in the Hundreds column: there are 2 options 123 and 132

With 2 you have 213 and 231

and with 3 you have 312 and 321

A total of 6.

Ken

Top

 Post subject: Posted: Sun Jun 08, 2008 7:55 pm
Dear Ken,

If you read the question (as we're always telling our kids!) you seem to be able to use the digits more than once. So you can have the 27 I think.

e.g.

111, 112, 121, 122, 113, 131, 133, 123, 132,

222, 212, 211, 221, 213,231, 233, 223, 232,

333, 311, 312, 321, 322, 331, 332, 323, 313

Something like that.

Regards,

Fm

Top

 Post subject: Posted: Sun Jun 08, 2008 8:32 pm

Joined: Fri Mar 17, 2006 5:12 pm
Posts: 1328
Location: Birmingham
Hi fm

You are quite correct - didn't spot you can reuse the digits

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 5 posts ]

 All times are UTC

#### Who is online

Users browsing this forum: Google Feedfetcher and 3 guests

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

Search for:
 Jump to:  Select a forum ------------------ FORUM RULES    Forum Rules and FAQs 11 PLUS SUBJECTS    VERBAL REASONING    MATHS    ENGLISH    NON-VERBAL REASONING    CEM 11 Plus GENERAL    GENERAL 11 PLUS TOPICS    11 PLUS APPEALS    11 PLUS TUTORS    INDEPENDENT SCHOOLS    11 PLUS CDs/SOFTWARE    11 PLUS TIPS    PRIMARY    SEN and the 11 PLUS    EVERYTHING ELSE .... 11 PLUS REGIONS    Berkshire    Bexley and Bromley    Birmingham, Walsall, Wolverhampton and Wrekin    Buckinghamshire    Devon    Dorset    Essex    Essex - Redbridge    Gloucestershire    Hertfordshire (South West)    Hertfordshire (Other and North London)    Kent    Lancashire & Cumbria    Lincolnshire    Medway    Northern Ireland    Surrey (Sutton, Kingston and Wandsworth)    Trafford    Warwickshire    Wiltshire    Wirral    Yorkshire BEYOND 11 PLUS    Beyond 11 Plus - General    GCSEs    6th Form    University