It is currently Tue Jan 16, 2018 1:36 pm

 All times are UTC

 Page 1 of 2 [ 11 posts ] Go to page 1, 2  Next
 Print view Previous topic | Next topic
Author Message
 Post subject: Decimal Questions I can't teach my ten year old??!Posted: Sat Aug 31, 2013 8:42 pm

Joined: Wed Nov 02, 2011 9:45 pm
Posts: 118
Hi All,

Please could someone tell me how to teach following Q'ds to a ten year old in a simple and fast way?

Much appreciated.

1.66.6 times 12.44

2. Divide 74.7 by 16.6

3.Represent 99/400 as a percentage

Thanks

Top

 Posted: Sun Sep 01, 2013 6:49 am

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8538
66.6x12.44

Multiply first number by 10 and second by 100 so you have two whole numbers to multiply together. Then divide the answer by 1000 at the end to get back to what it should have been.

74.7 div 16.6. Multiply both numbers by 10 and then do it. No need to adjust at the end because if you multiply or divide both numbers in a division calculation by the same number the answer remains the same.

99 div 400 as a percentage - multiply by 100

Top

 Posted: Sun Sep 01, 2013 8:39 am

Joined: Sat Dec 03, 2011 3:14 pm
Posts: 688
the easiest way to multiply decimals is to remove the decimal points and multiply them as normal multiplication sums and add the decimals afterwards.

66.6 times 12.44 - you would multiply 666 X 1244 and add the decimal point 3 places starting from the right. The question has 3 numbers after the decimal point in total (1 after 66 and 2 after 12) therefore the answer should also have 3 numbers after the decimal point.

so if I had 0.00004 X 0.1, the answers would be 0.000004 (the question has 5 numbers and 1 number after the decimal points, respectively). I just multiply 4 and 1 and count up the number of numbers after the decimal point and add the appropriate number of zeros after my decimal point.

**************

With division of decimals, the divisor should always be converted to a whole number before dividing.

So 2.5 divided by 0.005 would work as follows -

Write them out as a fraction for ease of understanding

the divisor/denominator has to be multiplied by 1000 to make it a whole number (0.005 X 1000 = 5)
whatever is done to the denominator has to be done to the numerator so 2.5 also has to be multiplied by a 1000 (2.5 X 1000 = 2500)

Finally, divide 2500 by 5 to give you 500 as the answer.

**********************

% are just special fractions of a 100

99 is the number out of 400 so write them out as a fraction and multiply by 100 to give you the %.

Another method is to use ratios

99 : 400
? : 100

400 divided by 4 gives you 100 so we divide 99 by 4 to give you the % of 24.75 (whatever you do to the Right-hand side has to be done to the left-hand side and vice versa)

*****************

Hope the explanations will help your child to understand these topics better. Decimals, fractions, ratios are used for a lot of other calculations as well so it is important to understand them really well.

Top

 Posted: Sun Sep 01, 2013 12:32 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13989
The method suggested above i.e. counting decimal points is not a good method!

An estimate will quiclly tell you the magnitude of the answer

66.6 x 12.44 is roughly 70 x 10 i.e under 1000.

Where have these questions come from! They are far more suitable for a calculator ....

Top

 Posted: Sun Sep 01, 2013 1:02 pm

Joined: Wed Nov 02, 2011 9:45 pm
Posts: 118
Hi all,

Appreciate all the methods suggested. I will try them out on my daughter.

The questions are from a mock exam which my daughter failed miserably and I am very anxious if these come in the real thing she will not pass so I need to teach her all the methods.

Do questions like this not come up in real thing???

Thanks all.

Top

 Posted: Sun Sep 01, 2013 1:05 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13989
Which exam? They are not KS2 appropriate questions.

Top

 Posted: Sun Sep 01, 2013 1:09 pm

Joined: Wed Nov 02, 2011 9:45 pm
Posts: 118
Hello Guest 55

I've pm'd you!

Top

 Posted: Sun Sep 01, 2013 8:30 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8538
I think it should be suitable to teach a ten year old who understands place value correctly how to multiply two decimal numbers together by multiplying them first by the correct number to get a whole number and the dividing by the correct number at the end, or by seeing what the correct order of magnitude for the answer should be for the answer and adjusting accordingly at the end.

It might not strictly be ks2, but goodness knows how one really defines that, but shouldn't be too difficult for a selective school child. We did it frequently at junior school.

Selection tests do not seem to be designed according to what is and is not ks2.

Top

 Posted: Mon Sep 02, 2013 2:12 pm

Joined: Mon Aug 12, 2013 9:13 am
Posts: 452
The decimal question is fairly straightforward - just multiply the numbers ignoring the decimals and then count/put the decimal place back into the answer.

Agree with mystery on KS2 syllabus which is just for reference however the tests are designed much tougher than that especially the ones for super selectives. I was shocked ot see that there's little or no algebra in KS2 and it is expected to solve equations by hit n trial which may take forever. There are tons of questions that I have seen which can be solved by algebra in seconds.

I suggest that the child should be extremely confident to convert decimals --> percentage--> fractions --> back to decimals.

Top

 Posted: Tue Sep 03, 2013 7:06 pm

Joined: Sat Dec 03, 2011 3:14 pm
Posts: 688
There is a very hazy line between KS2 and the exam questions. The syllabus might be KS2 but the questions and understanding of the syllabus is definitely of a much higher degree.

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 2 [ 11 posts ] Go to page 1, 2  Next

 All times are UTC

#### Who is online

Users browsing this forum: No registered users and 4 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