Q&A - PSLE Math

[dnsy]

Hi, need help on the following. Thanks in advance!


When a certain number of marbles in a box is divided equally among 5, 16 or 28 boys, there is a remainder of 4 marbles. What is the minimum number of marbles in the box?

[ck123]

tianzhu:

looking4Tutor:

http://i54.tinypic.com/2u6hf1s.jpg\">

Hi

Where is this question from?

Is the answer 38 circular shapes?

Best wishes

Is the answer 36 ?

[MathIzzzFun]

ck123:

tianzhu:

[quote=\"looking4Tutor\"]
http://i54.tinypic.com/2u6hf1s.jpg\">

Hi

Where is this question from?

Is the answer 38 circular shapes?

Best wishes

Is the answer 36 ?[/quote]Hi

tianzhu's answer is correct..

cheers.

[MathIzzzFun]

dnsy:

Hi, need help on the following. Thanks in advance!


When a certain number of marbles in a box is divided equally among 5, 16 or 28 boys, there is a remainder of 4 marbles. What is the minimum number of marbles in the box?

Hi

if we remove 4 marbles, then the remaining number of marbles will be divisible by 5, 16 and 28. So, the number of marbles = LCM of (5,16,28) + 4

cheers.

[dnsy]

Thanks MIZF. Understand it’s the LCM of (5,16,28)+4. But what is the working to derive to the answer, which is 564? If it is via trial and error, it will take a long time. Moreover, this is only a 1 mark question.

[gnagna]

tianzhu:

looking4Tutor:

http://i54.tinypic.com/2u6hf1s.jpg\">

Hi

Where is this question from?

Is the answer 38 circular shapes?

Best wishes

Hi Tianzhu
Can explain how you get 38?

[MathIzzzFun]

dnsy:

Thanks MIZF. Understand it's the LCM of (5,16,28)+4. But what is the working to derive to the answer, which is 564? If it is via trial and error, it will take a long time. Moreover, this is only a 1 mark question.

Hi

I know some schools teach their students how to find LCM...

http://i51.tinypic.com/2ufyu7q.jpg\">

If the student is not taught, then one would have to list the multiples or if this is a multiple choice question then one way is to divide each answer to check.

cheers.

[tianzhu]

gnagna:

Hi Tianzhu
Can explain how you get 38?

Hi

Good Morning.

This question appears friendishly easy at first glance.

But, it’s not so easy for PSLE kids.

Equal circles can be stacked in square or hexagonal packing such that each circle touches four or six others.

If you use square packing, you’ll get 36 circular shapes. With hexagonal packing, you’ll get 2 more circular shapes.

Best wishes

[ck123]

Hi tianzhu


How to teach the kid hexagonal packing? Any formula or pattern ?

Thanks for your enlightenment.

[tianzhu]

ck123:

Hi tianzhu


How to teach the kid hexagonal packing? Any formula or pattern ?

Thanks for your enlightenment.

Hi

You may use 50 cents coins to form the pattern as demonstration. If you pack the coins in hexagonal format, you’ll be able to pack them more densely.

Hope this helps.

Best wishes

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