Q&A - PSLE Math

[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!

[stary]

Dreamerz:

Hi I need help for these questions:


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!!

Hi!

2ECOND question:

1 - 9 -> 9 digits
10 - 99 -> 90 numbers -> 180 digits
Total -> 189 digits
Left -> 675 - 189 = 486 digits
Division -> 486/3 = 162
Pages -> 162 + 99 = 261

Best wishes!

[Alchemist]

vidhyalog:

tianzhu:

[quote=\"vidhyalog\"]Hi - Could somebody help me with this sum. From Punggol Primay Prelim 2011.


An egg seller had chicken eggs, duck eggs and quail eggs. He had 225 more quail eggs than duck eggs. After he had sold 60% of the chicken eggs, 2/3 of the duck eggs and 3 times as many quail eggs as duck eggs sold, he found that he had 25% of his quail eggs and a total of 205 eggs left. Find the total number of eggs he had first.

Hi

I’ll just provide some pointers for you to draw the MD.

Draw 3 boxes to show duck.
2 units of duck sold, left 1 unit.
For quail eggs, sold ------- 6 units (3 times), left ------2 units (25% left).

Draw a 5 smaller boxes or circles to show chicken.

From MD, we can see
5 units ----- 225
1 unit ----- 45

Number of eggs left ------ 2 boxes for chickens + 1 unit(duck) + 2 units (quail) ------205

Hence 2 boxes for chicken -----205 – (3*45)
1 box of chicken ------ 35

Total number of eggs he had first. ------ (11*45) + (5*35) -----670

Best wishes

[/quote]
Sorry Tianzhu - I am afraid I do not understand how to get 5 circles for chickens.
Thanks

[Tang]

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\">

Hi,

Sorry, I tried packing in hexagonal pattern, but only got 35 coins.

7 x 3 = 21
7 x 2 = 14
21 + 14 = 35

So it looks like 36 is the answer (12 x 3).

Someone may like to double-check and confirm what is the correct answer?