Go to navigation
It is currently Wed Dec 07, 2016 12:24 pm

All times are UTC




Post new topic Reply to topic  [ 12 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: Sun Jan 06, 2013 9:05 am 
Offline

Joined: Thu Oct 18, 2012 9:41 am
Posts: 434
Ben's father was 33 when Ben was born. 8 years ago Ben's father was twice as old as Ben is now. How old is Ben?

Any answers greatly appreciated

SleepyHead


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 10:57 am 
Offline

Joined: Tue Jan 17, 2012 4:29 pm
Posts: 63
Say, Ben is B and Father is F.
Say, B = x, and then F = (x+33).

Eight years ago it was like this:
(X+33) - 8 = 2x
X +33 - 8 = 2x
X + 25 = 2x
25 = 2x-x
25 = x

So Ben is now 25, and his Father is now 25+ 33 = 58. Eight years ago Father was 50, which is 25 x 2.

(No doubt, Father got lots of grey hair after pushing his DS Ben through selective exams ;) )


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 12:41 pm 
Offline

Joined: Thu Oct 18, 2012 9:41 am
Posts: 434
Excellent thanks, will explain to DD, who now thinks mummy can't do the 11+ :oops:


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 12:53 pm 
Offline

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11942
Use logic rather than algebra - algebra is not necessary!


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 2:26 pm 
Offline

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6966
Location: East Kent
diagrams help a lot too


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 5:29 pm 
Offline

Joined: Sun Sep 09, 2012 6:32 pm
Posts: 290
Guest55 wrote:
Use logic rather than algebra - algebra is not necessary!


Can you explain how you would do this using logic rather than algebra? I think in algebra - although obviously less formally - as does DS1. But DD is different and I wouldn't really know how else to explain it well to her.

Thanks.

_________________
The more that you read, the more things you will know.
The more that you learn, the more places you'll go.
Dr Seuss


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 6:09 pm 
Offline

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11942
Hi

Well I said the difference in their ages is 33 - but we are looking at one of them 8 years ago.

33 - 8 = 25

So effectively a difference of 25 - so that's Ben's age and his Dad then was 50.


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 10:24 pm 
Offline

Joined: Sun Sep 09, 2012 6:32 pm
Posts: 290
Thank you so much. That still took me ages to think through. I could see that you were right, but it still took me time to convince myself that there were no other options going that route. I think I have just proved the argument for why people need different methods to see which suits them best. If DD finds this sort of reasoning easier than algebra then I shall be back for some more help in a couple of years. It should be so obvious - maybe I am just tired? (Desperately trying to think of excuses for myself).

_________________
The more that you read, the more things you will know.
The more that you learn, the more places you'll go.
Dr Seuss


Top
 Profile  
 
PostPosted: Sun Jan 06, 2013 10:28 pm 
Offline

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11942
Age problems are always tricky - the algebra method would have been easier to follow if Ben's age = b so dad = b+ 33.

Using 'x' for the unknown just makes it harder! Always use letters that link with what they represent ..


Top
 Profile  
 
PostPosted: Mon Jan 07, 2013 7:25 am 
Offline

Joined: Tue Jan 17, 2012 4:29 pm
Posts: 63
Sorry, Guest55, I was using letters the way i did above as i was educated abroad and that was the way we were taught algebra - we were always using x for unknown. Hope no mistake there, just a matter of custom and convenience.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 12 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 forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
CALL 020 8204 5060
   
Privacy Policy | Refund Policy | Disclaimer | Copyright © 2004 – 2016