It is currently Tue Dec 06, 2016 4:03 pm

 All times are UTC

 Page 1 of 3 [ 23 posts ] Go to page 1, 2, 3  Next
 Print view Previous topic | Next topic
Author Message
 Post subject: BIDMASPosted: Wed Mar 09, 2016 8:04 am

Joined: Mon Feb 22, 2010 2:50 pm
Posts: 533
Using BIDMAS I get an answer of 2 for the following question. The actual answer is 8. Can some one explain why? Should I not be using BIDMAS or I am somehow using it incorrectly? Thank you

25-5x4+3

Top

 Post subject: Re: BIDMASPosted: Wed Mar 09, 2016 9:08 am

Joined: Mon May 16, 2011 1:05 pm
Posts: 4024
Using bidmas you would do the multiplication first to give you 25-20+3=8

Top

 Post subject: Re: BIDMASPosted: Wed Mar 09, 2016 10:41 am

Joined: Mon Feb 22, 2010 2:50 pm
Posts: 533
Tinkers wrote:
Using bidmas you would do the multiplication first to give you 25-20+3=8

But then shouldn't you do addition before subtraction which would give you 25-20+3 and then 25-23=2. I know that is wrong but still not sure why?

Top

 Post subject: Re: BIDMASPosted: Wed Mar 09, 2016 10:43 am

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11940
Hera wrote:
But then shouldn't you do addition before subtraction which would give you 25-20+3 and then 25-23=2. I know that is wrong but still not sure why?

You can't 'divorce' the sign and the number so doing addition first gives you 25 + 3 = 28 then 28 - 20 = 8

Top

 Post subject: Re: BIDMASPosted: Wed Mar 09, 2016 10:46 am

Joined: Mon Feb 22, 2010 2:50 pm
Posts: 533
Thank you. Got it now

Top

 Post subject: Re: BIDMASPosted: Wed Mar 09, 2016 11:43 am

Joined: Sat Jul 24, 2010 9:45 pm
Posts: 1488
Hera wrote:
Tinkers wrote:
Using bidmas you would do the multiplication first to give you 25-20+3=8

But then shouldn't you do addition before subtraction which would give you 25-20+3 and then 25-23=2. I know that is wrong but still not sure why?

Also, -20+3 will never give you -23. It is the same as +3-20, so -17. You would only get -23 if there was a bracket in there, in which case you would do the addition in the bracket first, i.e. -(20+3) = -(23) = -23

_________________
It felt like I hit rock bottom; suddenly, there was knocking from beneath... (anon.)

Top

 Post subject: Re: BIDMASPosted: Wed Mar 09, 2016 11:47 am

Joined: Fri Oct 11, 2013 8:55 am
Posts: 500
I think this query highlights quite a common misunderstanding of BIDMAS which is due to taking the acronym too literally.

Perhaps the simplest way to get it right is to be aware that, despite what the BIDMAS acronym seems to imply, there is no real ordering between "addition and subtraction". There is also no ordering between "division and multiplication".

So my advice would be if given a sum containing just addition and subtraction (or just multiplication and division) forget BIDMAS and just simply work it out left to right.

Top

 Post subject: Re: BIDMASPosted: Thu Mar 10, 2016 11:20 am

Joined: Sun May 09, 2010 12:04 pm
Posts: 2591
be aware that, despite what the BIDMAS acronym seems to imply, there is no real ordering between "addition and subtraction". There is also no ordering between "division and multiplication".

So my advice would be if given a sum containing just addition and subtraction (or just multiplication and division) forget BIDMAS and just simply work it out left to right.

important point!

Top

 Post subject: Re: BIDMASPosted: Thu Mar 10, 2016 11:26 am

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11940
I disagree - sometimes there is a 'most efficient way of calculating:

25 + 7 - 5 is best done in the order 25 - 5 + 7 which is quicker than tackling in order.

Top

 Post subject: Re: BIDMASPosted: Thu Mar 10, 2016 11:45 am

Joined: Sat Jul 24, 2010 9:45 pm
Posts: 1488
Guest55 wrote:
I disagree - sometimes there is a 'most efficient way of calculating:

25 + 7 - 5 is best done in the order 25 - 5 + 7 which is quicker than tackling in order.

Very true - that makes a much easier calculation. It relies, though, on a person remembering your original point - that a sign cannot be 'divorced' from a number. It took quite a while for my youngest to learn that the + or - sign belong to the numbers in front of which they are written, and stop ignoring the signs while re-ordering numbers in calculations.

_________________
It felt like I hit rock bottom; suddenly, there was knocking from beneath... (anon.)

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 3 [ 23 posts ] Go to page 1, 2, 3  Next

 All times are UTC

#### Who is online

Users browsing this forum: No registered users and 2 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