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maths question

Posted: Wed Mar 07, 2012 8:57 pm
by slush
Hi can someone help with this maths question.
2 dogs take 18 days to eat some dog food. how long will it take 3 dogs to eat the same amount of food.

thank you

Re: maths question

Posted: Wed Mar 07, 2012 9:00 pm
by Guest55
2 dogs take 18 days to eat some dog food. how long will it take 3 dogs to eat the same amount of food.
How long would the food last for one dog?

It would last 2 x 18 ie 36 days


So if there were 3 dogs ..36 divided by 3 = 12

Re: maths question

Posted: Thu Mar 08, 2012 8:25 am
by Okanagan
or put another way ⅔ of 18

the number of dogs is 1½ times what it was before -
so 18 / 1½ (or 3/2)
invert the fraction and change divide to multiply to get
18 x ⅔

Re: maths question

Posted: Thu Mar 08, 2012 7:37 pm
by Guest55
That's not a very clear method imho - inverse proportion needs explanation.

Re: maths question

Posted: Wed Mar 14, 2012 7:41 pm
by Elizabeth
If it takes 2 dogs 18 days, then on his own, it would take one dog 36 days.

Therefore, 3 dogs would divide the food equally 36 / 3 = 12.

It would take 12 days, as the other two have said.