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# Maths problem Tweet

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1. Maths problem
Susan has 2 dogs
Each dog is fed 3/8 kg of dog food each day.

Susan buys dog food in bags
Each bag weighs 14kg
For how many days can Susan feed the 2 dogs from 1 bag of dog food

You must show all your working.

I keep on getting 1 day but at the back of the book it says 18 days

I did 14/8 *6 = 10.5kg that clearly will only last one day I don't know what I'm doing wrong here.
2. Re: Maths problem
Why did you do 14/8*6 what was your thinking

Consider your units you have kg and kg/day

how can you combine those to give days
3. Re: Maths problem
How much is being used each day?
And how much is in each bag?
Divide the amount in the bag by the amount being used. (you don't seem to be doing that right).
4. Re: Maths problem
(Original post by TenOfThem)
Why did you do 14/8*6 what was your thinking

Consider your units you have kg and kg/day

how can you combine those to give days
8 parts in a bag and she's giving 3 a day to each dog so....
5. You should do 2*3/8 and then 14 divided by that answer. IE, 14/amount used in one day.

This was posted from The Student Room's iPhone/iPad App
6. Re: Maths problem
(Original post by zed963)
8 parts in a bag and she's giving 3 a day to each dog so....
There isn't 8 parts in a bag.
There's 8 parts in a kilogram. How many kilograms are in the bag?
7. Re: Maths problem
(Original post by zed963)
8 parts in a bag and she's giving 3 a day to each dog so....
So

8 parts in each kg and 14 kg gives how many parts in total?

Then she needs 6 of those each day so how many days?
8. Re: Maths problem

if she has two dogs and she feeds them both daily, then she feeds them kg of food every day

it is then a simple division
Last edited by DopeSk1llz; 04-06-2012 at 14:32.
9. Re: Maths problem
(Original post by TenOfThem)
So

8 parts in each kg and 14 kg gives how many parts in total?

Then she needs 6 of those each day so how many days?
18
10. Re: Maths problem
(Original post by zed963)
18
As the answers said
11. Re: Maths problem
(Original post by zed963)
8 parts in a bag and she's giving 3 a day to each dog so....
she's not giving 3/8 of the bag to each dog, she's giving 3/8 of a kilogram (375g) to each dog, so using 6/8 (750g) per day. There are 14kg in a bag, so 14kg / 0.75kg = 18 (and 2/3) days. Does this make any more sense?

As a general tip, try to apply a sanity test to your answers. 14 kilograms is a LOT of food. You've worked out that the dogs eat 10.5kg of food between them. That's a LOT of good, imagine the size of a tin! Does that sound likely/realistic? Since it doesn't, that might have given you a clue as to what had gone wrong.
12. Re: Maths problem
(Original post by zed963)
Susan has 2 dogs
Each dog is fed 3/8 kg of dog food each day.

Susan buys dog food in bags
Each bag weighs 14kg
For how many days can Susan feed the 2 dogs from 1 bag of dog food

You must show all your working.

I keep on getting 1 day but at the back of the book it says 18 days

I did 14/8 *6 = 10.5kg that clearly will only last one day I don't know what I'm doing wrong here.
Some Linear Programming should do the trick
13. Re: Maths problem
(Original post by GreenLantern1)
Some Linear Programming should do the trick
Really? To that extent? It a much simpler question than you think.
All you need to solve the problem is two calculations, Linear Programming would just make things more complex.
Last edited by jokosor; 04-06-2012 at 14:39.
14. Re: Maths problem
(Original post by Pkysam)
As a general tip, try to apply a sanity test to your answers.

We could have simply used a common sense approach

The dogs eat 6/8 = 3/4 of a kg each day

In 8 days they will have eaten 6 kg
So in 16 days they will have eaten 12kg

they have 2 kg left day 17 uses 3/4 and day 18 uses 3/4

we do not have 3/4 left
15. Re: Maths problem
(Original post by zed963)
Susan has 2 dogs
Each dog is fed 3/8 kg of dog food each day.

Susan buys dog food in bags
Each bag weighs 14kg
For how many days can Susan feed the 2 dogs from 1 bag of dog food

You must show all your working.

I keep on getting 1 day but at the back of the book it says 18 days

I did 14/8 *6 = 10.5kg that clearly will only last one day I don't know what I'm doing wrong here.
I did;
14/1 ÷ 3/8
Forgot about the fact it's a fraction for a minute. If you had a 14g bag, and a whole number portion then you'd automatically divide the bag by the portion. If the question said something like she has 14kg, and uses 2kg a day, you'd divide 14 by 2. When you have a fraction, all you have to do is make sure both of the numbers are fractions, that can easily be done by putting the whole number over one.
14/1 x 8/3 =
When dividing fractions, you can flip the second one and just times like normal.
112/3 = 37
You then get a fraction which can be divided. It ends up as 37 point something, always round it down if you're dealing with something like this.
37 ÷ 2 = 18 days
Two dogs, so divide by two.

Probably an easier method, but that's what my instinct told me to do. ;D
Last edited by Deziah; 04-06-2012 at 14:49.
16. Re: Maths problem
(Original post by jokosor)
Really? To that extent? It a much simpler question than you think.
All you need to solve the problem is two calculations, Linear Programming would just make things more complex.
Na linear programming is easy. He is clearly having problems with calculations. Draw the two lineds you create and find the intersection.

Simples.
17. Re: Maths problem
(Original post by GreenLantern1)
Na linear programming is easy. He is clearly having problems with calculations. Draw the two lineds you create and find the intersection.

Simples.
What equations would you use for your lines?
18. Re: Maths problem
Did you work it out then?
19. Re: Maths problem
(Original post by GreenLantern1)
Did you work it out then?
LoL

Post 9

Just before you joined us

20. Re: Maths problem
(Original post by TenOfThem)
LoL

Post 9

Just before you joined us

Ahahah I always come late for these things! And it is always Zed963