Q&A - PSLE Math

[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

http://farm7.static.flickr.com/6176/6146554898_54f4db9088_z.jpg\">

[tianzhu]

looking4Tutor:

Thank you, tianzhu.

Hi

You're welcome.

Best wishes

[Dreamerz]

Hi I need help for these questions:


1) Tap A can fill up an empty tank in 20 minutes and Tap B can empty it the full tank completely in 12 minutes. Both taps were turned on at the same when the tank is 1/2 filled. how long does it take for the tank to be completely emptied?

2)Mrs Lim’s son helped her to type the page numbers of her new book. He noticed that different pages required different numbers of digits. He counted that there were a total of 675 digits. How many pages were there in the book?

thank you in advance!!

[stary]

Dreamerz:

Hi I need help for these questions:


1) Tap A can fill up an empty tank in 20 minutes and Tap B can empty it the full tank completely in 12 minutes. Both taps were turned on at the same when the tank is 1/2 filled. how long does it take for the tank to be completely emptied?

thank you in advance!!

Hi!

F1RST Question:

Difference->1/12 - 1/20 = 1/30 tank per min
Time -> 1/2 (Divide by) 1/30 = 15 min

Best regards!