Confusing maths problem

[Pauldohert]

No you are still wrong!

Try 26x + 18y = 44


Your same logic could be applied to use the subtitution in this

x = 26/18y


But that doesn't give you the answer x = 1, y = 1 !!!!

Simlilary you didn't get 4 and 22 in the original problem - why? because your logic for getting the substitution is off.

 

[Big Pat]

I do follow the logic of that, but the ~ rather than the = seems a problem. 26/18 ~ 1.44. Isn't approximating going to give fractions in the result, e.g. 13.3 cakes?

 

[Pauldohert]

I do follow the logic of that, but the ~ rather than the = seems a problem. 26/18 ~ 1.44. Isn't approximating going to give fractions in the result, e.g. 13.3 cakes?

The ~ is ok if you work it out - it was the original substitution that was made that was not logical and incorrect , it happened to give the correct answer, but won't in
26x + 18y = 44, though the substitution should be valid in both!

 

[chergh]

No you are still wrong!

Try 26x + 18y = 44


Your same logic could be applied to use the subtitution in this

x = 26/18y


But that doesn't give you the answer x = 1, y = 1 !!!!

Simlilary you didn't get 4 and 22 in the original problem - why? because your logic for getting the substitution is off.

Yep your absolutley right, it's just a coincidence it works for this particular case. Hate it when that happens

Thinking about it is actually a very silly mistake, mistake in the logic was that you can't actualy express the quantity of cakes in terms of the quantity of choclate they are completely independent of each other.

 

[Big Pat]

And the answer is...

I spoke to my daughter's maths teacher who says the method is:

• Simplify the ratio as much as possible, in this case to 13:9.
• Then you know (!!!?) that you must have 13 of one or the other.
• Mutiply 13*26p to give £3.38.
• Subtract £3.38 from £5.00 to leave £1.62.
• Divide £1.62 by 18 to give exactly 9.
• It works, so those are the right answers!

I feel very dissatisfied by this, but she says that as the kids haven't really been taught much iin the way of fractions or decimals yet, you have to assume that "the answer is in the ratio".

She was completely surprised when I told her there was ANOTHER correct answer (4 and 22) and I think she was only barely able to work out in her head that I was actually correct. Her response to this was "not to worry" as the child is only expected to come up with one right answer.

Frankly, I'm appalled!

 

[Pauldohert]

I spoke to my daughter's maths teacher who says the method is:

Simplify the ratio as much as possible, in this case to 13:9.
Then you know (!!!?) that you must have 13 of one or the other.
Mutiply 13*26p to give £3.38.
Subtract £3.38 from £5.00 to leave £1.62.
Divide £1.62 by 18 to give exactly 9.
It works, so those are the right answers!
I feel very dissatisfied by this, but she says that as the kids haven't really been taught much iin the way of fractions or decimals yet, you have to assume that "the answer is in the ratio".

She was completely surprised when I told her there was ANOTHER correct answer (4 and 22) and I think she was only barely able to work out in her head that I was actually correct. Her response to this was "not to worry" as the child is only expected to come up with one right answer.

Frankly, I'm appalled!

Yes the teacher has it wrong. Demonstated by the fact she "missed" an answer.

Also 26x + 18y = 44

so the ratio is
13:9 so there must be 13 in of one! errrm no! In the problem posed the 13 was lucky, and illogical. But correct!

I wouldn't worry about the teacher, not at age nine, if it was a specialist maths teacher at 11+ obviously you should be appalled.

I suspect this particluar problem was lifted from some text book, where the author knew some weird and wonderful incorrect methods could seem to "calculate" the right answer.