Q&A - PSLE Math

[Mum1113]

Thanks tianzhu....as usual the illustration is impressive !


Will u get to the other one as well ?
Qn: There are some red and blue pencils in a box. If 30 red pencils are taken out from the box, the total number of pencils left will be 8 times the number of red pencils left. If 50 blue pencils are taken out from the box, the total number of pencils left will be thrice that of blue pencils left. How many pencils are there in the box ?

[tianzhu]

Mum1113:

Thanks tianzhu....as usual the illustration is impressive !

Will u get to the other one as well ?

Hi

You're welcome.

Here's the answer to your second question.

Hope this helps.

Best wishes

http://farm6.static.flickr.com/5147/5736014129_4b0176859f_z.jpg\">

[Mum1113]

thanks tianzhu, the colorful picture makes digestion easier (I don't mean dinner but the problem sum), cheers

[tianzhu]

Mum1113:

thanks tianzhu, the colorful picture makes digestion easier (I don't mean dinner but the problem sum), cheers

Hi Mum1113

Good Morning.

You're welcome.

Best wishes

[chrisu]

There are 800 children in Group A. 30% of the children in Group A were boys. There were 400 children in Group B. 60% of the children in Group B were boys. After some transfer between the two groups, 25% of the children in Group A and 75% of the children in Group B were boys. What is the transfer from Group B to A?


Note : My answer is 70 Girls were transfer from B to A. 30 Boys were transfer from A to B, though not needed. I got the answer using algebra and simultaneous equation which my daughter do not understand well.

Anyone can do with models or other easier to understand method. Thank you.

[Neat]

tianzhu:

Hi


A quick one for Q1

One needs to differentiate the ratios representing the number of legs and the number of animals. The ratios for the number of legs and the number of animals are of different measures.

The total number of ducks' legs to the total number of cows' legs is 5:9 ------ 20:36 (equivalent ratios)

A duck ----- 2 legs, a cow ----- 4 legs

This means the total number of ducks to the total number of cows ----- 10:9 -----20:18

Ducks ----- 20
Cows ----- 18

There are 38 ducks and cows.

Best wishes

[quote]tianzhu

What made you decide to multiply by 4 to get the equivalent ratio?

Pls enlighten.
[/quote]

[tianzhu]

Neat:

What made you decide to multiply by 4 to get the equivalent ratio?

Hi

We are given that the total number of ducks and cows is between 20 and 40.

We are also given the ratio of the total number of ducks' legs to the total number of cows' legs is 5:9.

Given this ratio, a student is expected to find out the number of animals.

A cow has 4 legs and a duck has 2 legs.

Hence, the number showing the number of cow’s legs has to be a multiple of 4.Likewise the number showing the number of duck’s legs has to be a multiple of 2.

That’s why we multiply the given ratios 5:9 by 4 to get 20:36.

This gives us 10:9 as the ratio for the number of ducks to the number of cows. This is not within the range of 20 and 40.

Multiply by 2 to get an equivalent ratio of 20:18 which is 38 and within the range.

Best wishes

[tianzhu]

Hi


In this question, a student should note that the total number of boys and girls remains the same before and after the transfer.

We have two unknowns and two equations.

Students who are taught SE by their tutors or parents may use them.

For those without knowledge of SE, they may solve the equations pictorially or use letters of the alphabets as representation. Alternatively, they may also use units and parts as representation.

Best wishes

http://farm6.static.flickr.com/5263/5738959768_cab69b70e7_z.jpg\">

[chrisu]

Hi Tianzhu,


I'm dead clear with your pictorial! Thanks a lot. :boogie:

tianzhu:

Hi

In this question, a student should note that the total number of boys and girls remains the same before and after the transfer.

We have two unknowns and two equations.

Students who are taught SE by their tutors or parents may use them.

For those without knowledge of SE, they may solve the equations pictorially or use letters of the alphabets as representation. Alternatively, they may also use units and parts as representation.

Best wishes

http://farm6.static.flickr.com/5263/5738959768_cab69b70e7_z.jpg\">

[shurley197323]

Pls help. A container has a mass of 1 4/5kg when it is completely filled with sweets.It has a mass of 1 3/10kg when 3/8 of the sweets are removed. What is the mass of the container when it is empty ?

Many thanks.