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 Post subject: GL Math Question
PostPosted: Sun Aug 18, 2019 3:49 pm 
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Joined: Wed Jan 31, 2018 11:37 pm
Posts: 14
GL Maths Pack 1, Paper 1, Question 48
The clock shows twenty past twelve. What is the smaller angle formed by the hands?
Answer: 120 degrees

But this is wrong. As the long hand moves, so does the short hand. It's easy to see that when the long hand points 20 minutes, the short one must have moved by 10 degrees, so the actual answer is 120-10 = 110 degrees. Am I missing something, or is this topic taught without the above consideration (i.e. just use the first-order approximation, and ignore the small movement of the short hand)?


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 Post subject: Re: GL Math Question
PostPosted: Sun Aug 18, 2019 4:23 pm 
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Joined: Sat Oct 13, 2018 4:00 pm
Posts: 312
I don't think 11 year olds will know how many degrees the hour hand moves in 20 minutes in a question that they have one minute to answer. Plus, the answers are multiple choice. Did 110 appear in the choices?!


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 Post subject: Re: GL Math Question
PostPosted: Sun Aug 18, 2019 4:28 pm 
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Joined: Wed Jan 31, 2018 11:37 pm
Posts: 14
Deb70 wrote:
I don't think 11 year olds will know how many degrees the hour hand moves in 20 minutes in a question that they have one minute to answer. Plus, the answers are multiple choice. Did 110 appear in the choices?!


Yes, 110 was a choice. DS went with 120, which was the correct choice based on the key.
I wanted to explain why the whole thing was wrong but then I thought it would confuse him, so I let it go.


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 Post subject: Re: GL Math Question
PostPosted: Mon Aug 19, 2019 9:06 am 
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Joined: Sat Aug 10, 2013 11:46 am
Posts: 243
If you look at this section of the forum, there do seem to be a few badly worded or badly thought through questions that crop up. I think all you can do is hope none are in the actual 11+.
I know similar questions have been in the UKMT junior maths challenge, aimed at years 7 to 9, where they are supposed to take the movement of the hour hand into account.
However, for the 11+, I think Deb is right.


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