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 Post subject: math problemPosted: Fri Nov 16, 2007 9:45 pm
If it takes 8 minutes to drill 6 holes, how many holes can be drilled in 15 minutes

Could someone explain how work out the above question?

thanks for any help

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 Post subject: Posted: Sat Nov 17, 2007 6:23 pm

Joined: Thu Nov 08, 2007 9:57 pm
Posts: 1167
.

Last edited by Belinda on Wed Oct 31, 2012 9:53 pm, edited 1 time in total.

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 Post subject: Posted: Sat Nov 17, 2007 10:34 pm

Joined: Fri Sep 07, 2007 1:12 pm
Posts: 151
Firstly, I'm no expert but I would explain it the way my brain worked it out.

An obvious number fact is that 16 is double 8. Therefore, we know that 12 holes could be drilled in 16 mins as we have only been given 15 mins we would take the last drilled hole away! The answer therefore has to be 11.

I am assuming the answer has to be in whole holes!!

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 Post subject: Posted: Sun Nov 18, 2007 9:49 am

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13989
Belinda,

Your method is called the 'unitary' method as you are finding out how much '1' is by dividing then multiplying to get what you need. It works well for most children!

I like the 'approx' method above to - in a MC situation it would probably be good enough.

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 Post subject: HolesPosted: Tue Nov 20, 2007 9:00 am
stly, I'm no expert but I would explain it the way my brain worked it out.

An obvious number fact is that 16 is double 8. Therefore, we know that 12 holes could be drilled in 16 mins as we have only been given 15 mins we would take the last drilled hole away! The answer therefore has to be 11.

I am assuming the answer has to be in whole holes!!

I would say 12 holes rather than 11 - you have started on the 12th so you do have a hole, even if it's smaller than you are aiming for!

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 Post subject: Posted: Tue Nov 20, 2007 8:05 pm
I agree. Maths says you have 11.25 holes but common sense says you have 12 holes, the 12th one being less deep.

Is this an ill-thought-out question or a trick one?

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 Post subject: Posted: Tue Nov 20, 2007 10:01 pm

Joined: Tue Dec 13, 2005 12:49 pm
Posts: 1647
Location: berkshire
Aha....would .25 be a full hole or just a dent????

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 Post subject: Posted: Tue Nov 20, 2007 10:50 pm
I think it's a badly thought out question - you could make a case for 11 or 12 and the last thing you want to do under pressure is worry about which one the examiner had in mind.

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