Maths problem

[Premacist]

I think this is not sec sch math, P6 students are expected to do this type of question in the PSLE.

 

 

wah lau.

 

A= ( B+c+92)/3

 

b = (A+C+92)/4

 

C = ( A+ B+92)/5

 

solve lor.

 

sec sch math nia leh

 

[Little_prince]

This is PSLE question, I ask my son who is taking his PSLE this year to do, he told me Alan have 375 stamps at first. Is that the correct answer?

 

 

i got A=195. becky got 135?

 

yes i do by simultaneous equations

 

dunno how to explain using model method

 

pri school standard leh

 

cannot solve like that

psle ah?

 

wah kaoz... then i dunno liao lol

[Premacist]

My son said your answer is wrong because:

 

if alan has 195, he needs to give away 2/3 of B -->90, He will has balance of 105.

 

If Beck has 135, he needs to give away 2/5 of A -->78, He will has balance of 57.

 

The balance not equal lah.

 

i got A=195. becky got 135?

psle ah?

 

wah kaoz... then i dunno liao lol

 

[Little_prince]

My son said your answer is wrong because:

 

if alan has 195, he needs to give away 2/3 of B -->90, He will has balance of 105.

 

If Beck has 135, he needs to give away 2/5 of A -->78, He will has balance of 57.

 

The balance not equal lah.

 

 

lol. that would explain why I didn't get into RI.

 

better leave the teaching to my wife then

[1fast1]

how to do by model method?

 

Allan had 60 stamps more than Becky. They each gave away some stamps. Becky gave away 2/5 of the number Allan had at first. Allan gave away 2/3 of the number Becky had at first. Both had an equal number of stamps left. How many stamps Allan have at first?

 

thanks guys.

 

Here's a model method, but like all these so-called "simple heuristics" it becomes helluva more complicated than just doing the damn algebra.

 

See attachment. Should be self explanatory. The reason I chose 15 units for Becky was because this is the lcm of 3 and 5, the denominators in the given fractions.

 

So Alan gives away 2/3*15 = 10 units, leaving him 5 units + 60 stamps left.

 

And Becky gives away 2/5 of what Alan had at the start (which is 15 units + 60 stamps), so she gives away 2/5*15 units + 2/5*60 stamps = 6 units + 24 stamps. She therefore has 15 units - (6 units + 24 stamps ) = 9 units - 24 stamps left.

 

So equate those:

 

5 units + 60 stamps = 9 units - 24 stamps

 

Hence 4 units = 84 stamps

 

1 unit = 21 stamps

 

Therefore Alan had 15*21 + 60 = 375 stamps at the beginning.

 

I don't know if this is sufficiently "model-like" but in the end algebra-like manipulation is still needed (except we're calling them "units" instead of 'x'). You can beautify the model by subdividing B into 15 boxes and moving things around.

[Enye]

 

Here's a model method, but like all these so-called "simple heuristics" it becomes helluva more complicated than just doing the damn algebra.

 

See attachment. Should be self explanatory. The reason I chose 15 units for Becky was because this is the lcm of 3 and 5, the denominators in the given fractions.

 

So Alan gives away 2/3*15 = 10 units, leaving him 5 units + 60 stamps left.

 

And Becky gives away 2/5 of what Alan had at the start (which is 15 units + 60 stamps), so she gives away 2/5*15 units + 2/5*60 stamps = 6 units + 24 stamps. She therefore has 15 units - (6 units + 24 stamps ) = 9 units - 24 stamps left.

 

So equate those:

 

5 units + 60 stamps = 9 units - 24 stamps

 

Hence 4 units = 84 stamps

 

1 unit = 21 stamps

 

Therefore Alan had 15*21 + 60 = 375 stamps at the beginning.

 

I don't know if this is sufficiently "model-like" but in the end algebra-like manipulation is still needed (except we're calling them "units" instead of 'x'). You can beautify the model by subdividing B into 15 boxes and moving things around.

 

thanks

 

seems like a "simpler" form of algebra

 

guess model method has its limits

 

[Ender]

My method although looks like modelling, but actually it's substitution in disguise. Just need to find relationship between A and B, i.e B=A+30, and substitute it in.

[Little_prince]

My method although looks like modelling, but actually it's substitution in disguise. Just need to find relationship between A and B, i.e B=A+30, and substitute it in.

 

wah. must praise you for your effort.

 

even dumb math idiot like me can understand

[Enye]

My method although looks like modelling, but actually it's substitution in disguise. Just need to find relationship between A and B, i.e B=A+30, and substitute it in.

 

thanks

[1fast1]

After seeing all these so-called "simple heuristic" solutions, I have to ask: why the f**k are our educators so bloody dumb?

 

These problems are handled much more efficiently with simple algebra. So why expect people to come up with convoluted methods to solve the same problem in the name of a fad?

 

To screw something in, we use a screwdriver, not a hammer. But our educators seem to be the sort who would teach our kids to use a hammer "just because".

 

Right now Singapore is still ranked highly in academic terms. Keep in mind that a lot of this is from past performance and traditional curricula. But if these jokers are allowed to carry on with these new-fangled fads, I see our general mathematical literacy dropping relative to the other nations.

Edited June 6, 2014 by Turboflat4

[Sosaria]

I think the main reason given by educators about why they don't want to intro algebra too early is because kids do not yet fully understand what are those "x" and "y" and whatnot.

 

In effect they are just told to 'let this be x' and 'let that be y', follow some procedures to eliminate one unknown and then the other. Supposedly the kids learn nothing about math, especially for those weak in the subject.

 

Model gives them a 'visual' and can be represented physically, I suppose. (But how about those learners who are not visual-learner types??)

[OmOm]

Bro, you have hit the nail right on the head. The earlier post that you made achieved what the entire Ministry of Education has failed to do in the last thirty years - connecting the "arcane" to daily living, showing how relevant mathematics is to our day-to-day activities.

 

Without understanding the fundamental reason for learning mathematics, or for that matter any other aspect of modern-day education, how can the student even begin to appreciate the relevance of his learning to life, much less the inherent beauty that lies in these subjects?

 

"Just because" has become the mantra for our educators and their bureaucratic superiors. They conveniently ignore the fact that there are many ways to skin a cat, many methods of solving problems, and choosing instead to pat themselves on the back for past stellar performances while turning a blind eye to present-day social issues that are arising from their policies and decisions.

 

After seeing all these so-called "simple heuristic" solutions, I have to ask: why the f**k are our educators so bloody dumb?

 

These problems are handled much more efficiently with simple algebra. So why expect people to come up with convoluted methods to solve the same problem in the name of a fad?

 

To screw something in, we use a screwdriver, not a hammer. But our educators seem to be the sort who would teach our kids to use a hammer "just because".

 

Right now Singapore is still ranked highly in academic terms. Keep in mind that a lot of this is from past performance and traditional curricula. But if these jokers are allowed to carry on with these new-fangled fads, I see our general mathematical literacy dropping relative to the other nations.

 

[1fast1]

I think the main reason given by educators about why they don't want to intro algebra too early is because kids do not yet fully understand what are those "x" and "y" and whatnot.

 

In effect they are just told to 'let this be x' and 'let that be y', follow some procedures to eliminate one unknown and then the other. Supposedly the kids learn nothing about math, especially for those weak in the subject.

 

Model gives them a 'visual' and can be represented physically, I suppose. (But how about those learners who are not visual-learner types??)

 

I am decidedly not a "visual person". I am extremely left brain dominant. When it comes to rotating complicated 3-D shapes in my head, for instance, I actually find it easier to map the vertices to numbers and then think about the transformation that the rotation implies! Believe it or not, this is how I managed to score highly even on visuo-spatial/perceptual IQ tests. Of course the raw numerical/verbal components were a doddle.

 

So I will admit that I may be biased against this drive for personal reasons. But the thing is this: most people with high mathematical ability tend *not* to be visual learners either. In fact, teaching math with this much emphasis on visual representation is akin to trying to fit a square peg into a round hole. While this sort of teaching may appeal to the lowest common denominator of students who are traditionally weaker at symbolic manipulation (classic methods), it might alienate those whose brains work differently.

 

There is a definite role for visual representation in mathematical teaching. Elementary set theory, for instance, is very difficult to introduce without drawing Venn diagrams. Of course, students will later have to formalise their learning using axioms like Zermelo-Fraenkel (with the Axiom of Choice) and propositional logic based on laws like De Morgan's law etc. But the way they're trying to shoehorn complicated word problems into visual models rubs me the wrong way. Of course, curve sketching and plotting are critical in real analysis. Other than that, very little higher level maths relies primarily on visual representations. There are some notable exceptions, e.g. graph theory, but not the sort of math that even technical people would expect to apply daily.

Edited June 6, 2014 by Turboflat4

[Ender]

another one

 

A,B,C and D each have some money.

 

A has 1/3 of the total B, C and D have.

 

B has 1/4 of the total A, C and D have

 

C has 1/5 of the total A, B and D have

 

D has $92.

 

How much do they have in total?

 

I consulted a primary 6 student on this, actually my collick post this question to his P6 daugther, and this is her answer. I modded it with extra wordings for easy understanding,

 

A,B,C and D each have some money.

A has 1/3 of the total B, C and D have. -----(1)

B has 1/4 of the total A, C and D have ------(2)

C has 1/5 of the total A, B and D have ------(3)

D has $92.

From (1) A:BCD => 1:3 Total is 4 shares

From (2) B:ACD => 1:4 Total is 5 shares

From (3) C:ABD => 1:5 Total is 6 shares

Remember (1)=(2)=(3), common mulitple for 4, 5 and 6 = 60

From (1) A:BCD => 15:45 (X15)

From (2) B:ACD => 12:48 (X12)

From (3) C:ABD => 10:50 (X10)

Now they all share common units.

ABD = 50 units

A+B = 27 units

therefore D=50-27=23 units

We know D=$92 and is 23 units,

Therefore 1 unit is $4

Altogether is 60 units, i.e 60X4= $240

Edited June 6, 2014 by Ender

[Enye]

 

I consulted a primary 6 student on this, actually my collick post this question to his P6 daugther, and this is her answer. I modded it with extra wordings for easy understanding,

 

A,B,C and D each have some money.

A has 1/3 of the total B, C and D have. -----(1)

B has 1/4 of the total A, C and D have ------(2)

C has 1/5 of the total A, B and D have ------(3)

D has $92.

From (1) A:BCD => 1:3 Total is 4 shares

From (2) B:ACD => 1:4 Total is 5 shares

From (3) C:ABD => 1:5 Total is 6 shares

Remember (1)=(2)=(3), common mulitple for 4, 5 and 6 = 60

From (1) A:BCD => 15:45 (X15)

From (2) B:ACD => 12:48 (X12)

From (3) C:ABD => 10:50 (X10)

Now they all share common units.

ABD = 50 units

A+B = 27 units

therefore D=50-27=23 units

We know D=$92 and is 23 units,

Therefore 1 unit is $4

Altogether is 60 units, i.e 60X4= $240

 

 

Thanks!

[Porker]

After seeing all these so-called "simple heuristic" solutions, I have to ask: why the f**k are our educators so bloody dumb?

 

These problems are handled much more efficiently with simple algebra. So why expect people to come up with convoluted methods to solve the same problem in the name of a fad?

 

To screw something in, we use a screwdriver, not a hammer. But our educators seem to be the sort who would teach our kids to use a hammer "just because".

 

Right now Singapore is still ranked highly in academic terms. Keep in mind that a lot of this is from past performance and traditional curricula. But if these jokers are allowed to carry on with these new-fangled fads, I see our general mathematical literacy dropping relative to the other nations.

 

Good one pundek. The simplest solution is always the most elegant one.

[Kb27]

Maths give me a headache now, even though I use to score well in school.

 

Very strenuous on the brain cells.

[nazerath]

I even got the car park one wrong!! I avoided looking at the above questions least I get them all wrong! terrible for the confidence.