It is currently Tue Jan 16, 2018 9:23 am

 All times are UTC

 Page 1 of 1 [ 4 posts ]
 Print view Previous topic | Next topic
Author Message
 Post subject: Help maths questionPosted: Tue Oct 14, 2008 7:11 pm

Joined: Tue Oct 14, 2008 7:06 pm
Posts: 3
Can anyone help with a quick method to work out questions like the one below:

Two Whole number are each between 50 and 70
They multiple to make 4095
write in the missing numbers
___ X ___ = 4095

thanks

Top

 Post subject: Posted: Tue Oct 14, 2008 7:55 pm

Joined: Thu Jul 10, 2008 9:56 pm
Posts: 81
Think of the units....... The "unit" digit of one number multiplied by the second "unit" digit must result in another number which has 5 for units. As far as I can see one of the numbers has to end in a 5. Therefore you only have to think about two numbers.... 55 and 65 .....

By estimating you can see that it is more likely to be 65 than 55 so try that one first.....

4095 / 65 = 63

The answer will therefore be 63 x 65 = 4095

The "unit" trick is good for checking long multiplication (what I mean by this is if you have a number 4562 x 5467 your answer is bound to end in a 4 because 2 x 7 is 14 ) and also for multiple choice exams although some papers I noticed have all options ending in the same digit!

So, in answer to your question, look for the units first to see if it would give you a clue.

Top

 Post subject: Posted: Tue Oct 14, 2008 8:10 pm
I agree that the giveaway was the fact it ended in 5. However, if it did not, trial and error would be harder.

The other way of doing it is to work it out as a product of prime factors.

4095 = 3 x 3 x 5 x 7 x 13

then group accordingly 5 x 13 (65) and 3 x 3 x 7 ( 63).

This technique would work for all questions of this type.

Top

 Post subject: Posted: Wed Oct 15, 2008 8:59 am

Joined: Tue Oct 14, 2008 7:06 pm
Posts: 3

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 4 posts ]

 All times are UTC

#### Who is online

Users browsing this forum: No registered users and 1 guest

 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