Go to navigation
It is currently Sun Dec 04, 2016 10:18 am

All times are UTC




Post new topic Reply to topic  [ 14 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: isosceles triangle
PostPosted: Sat Jan 09, 2016 10:47 am 
Offline

Joined: Sat Jan 09, 2016 10:32 am
Posts: 5
can anyone help to solve this problem?
In an isosceles triangle, twice one of the angles is 5 times as big as another. What is not a possible size for one of the angles?
The options are 100, 75,40,30,20


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 11:37 am 
Offline

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6965
Location: East Kent
In an isosceles triangle 2 of the angles are the same.
You can use this fact and trial and error.

Also you cannot exceed the maximum number of degrees in a triangle.


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 12:04 pm 
Offline

Joined: Tue Oct 27, 2009 8:19 pm
Posts: 6255
Here the answer is 20 apparently :D


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 1:24 pm 
Offline

Joined: Sun Oct 19, 2014 11:52 am
Posts: 60
and using algebra...

If,

x = the size of one of the equal pair of angles.
y = the third angle.

We have two sets of equations (possibilities):

2x = 5y
2x + y = 180
OR
2y = 5x
2x + y = 180


Solving first pair, we get
x = 75
y = 30

Solving second pair, we get
x = 100
y = 40

Hence, the remaining i.e 20, must be the answer.


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 1:38 pm 
Offline

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11934
target 2016 - Algebra makes this harder and is not appropriate for this question.

SImple trial and improvement gets the answer in a few seconds.


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 1:48 pm 
Offline

Joined: Sun Oct 19, 2014 11:52 am
Posts: 60
It's a matter of choice. There is no one way, but this way makes it show how we arrived at the answer better. Personally I don't like "trial and error"... takes me ages!


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 2:02 pm 
Offline

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11934
As mathematicians we judge the best method as the shortest and most elegant - the choice of x and y also makes it harder to remember which variable is which. Note I said trial and improvement - not error!

e = equal angle would have been a better choice.


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 2:08 pm 
Offline

Joined: Sun Oct 19, 2014 11:52 am
Posts: 60
Now that's getting pedantic. Like I said - it's a matter of choice :D


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 2:09 pm 
Offline

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6965
Location: East Kent
I would expect most children in y5/6 to solve it without algebra.

Agree trial and improvement, rather than error :oops:


Top
 Profile  
 
 Post subject: Re: isosceles triangle
PostPosted: Sat Jan 09, 2016 2:13 pm 
Offline

Joined: Sun Oct 19, 2014 11:52 am
Posts: 60
try again! :wink:


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 14 posts ]  Go to page 1, 2  Next

All times are UTC


Who is online

Users browsing this forum: No registered users and 3 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