Q&A - PSLE Math

[Lynn2]

Hi Dharma,


Thank you for showing me another way in looking at this question.

Will walk thr the various methods that ksp has worked out and see whether she can see it.She believe in able to understand it rather than route learning.


Thanks.



cheers

Dharma:

Lynn2:

Hello all,

Can someone pls help this question.Have tried to teach dd to use set method to do this question, but always ended up using guess and check which is very time consuming.She cannot understand the explanation even I tried .

Any kind soul can help?
Here it goes:

1 Box A contains 50 cent coins and Box B contains $1 coins.Box A contains 17 more coins than Box B.The amount of money in Box A is $15.50 less than in Box B.Find the total amount of money in the boxes

Thanks and sure hope dd can clear this type of question.

Cheers
Lynn2

Difference in number of coins => 1u - 1p = 17
Difference in the value of the coins => 100cents (1p) – 50(1u) = 1550
100p - 50u = 1550
2p – 1u = 31
1p = 17 + 31 = 48
1u = 48 + 17 = 65

Total amount of money = (65) x 50 cents + (48 ) x 100 cents = 8050 cents = $80.50

[Dharma]

Lynn2:

Hi Dharma,


Thank you for showing me another way in looking at this question.

Will walk thr the various methods that ksp has worked out and see whether she can see it.She believe in able to understand it rather than route learning.


Thanks.

No worries Lynn2.
Your girl definately has the right attitude towards learning. Good luck!

[Lynn2]

Hi Dharma,


Thank you.

She used to do math via rote learning, only realised that it din work when her math dropped terribly.

Recently, she hit high 90s cos she starts to have process skill....hahaha.That is why she insists that she must understand the method before she can accept it.I dont understand why this \"coin' type of question is always her blind spot.Is there a way to change the \"coin\"to something else as a question?


Cheers

Dharma:

Lynn2:

Hi Dharma,

Thank you for showing me another way in looking at this question.

Will walk thr the various methods that ksp has worked out and see whether she can see it.She believe in able to understand it rather than route learning.


Thanks.

No worries Lynn2.
Your girl definately has the right attitude towards learning. Good luck!

[tianzhu]

Lynn2:

I dont understand why this \"coin' type of question is always her blind spot.Is there a way to change the \"coin\"to something else as a question?

Hi

Instead of coins, you may use stamps or phone cards of different values.

How about trying on this questions about stamps?

Xie Ming Ming paid $36 for some 10 cents and 20 cents stamps. She bought 4 times as many 10 cents stamps as 20 cents stamps. How many stamps did she buy altogether?

In your question, the proportion of each type of coins are given, this simplifies the solution to a certain extent.

The concept of grouping or set is commonly used to solve such question. You may also use MD or Number* Value method. Although, the presentation may varies, but alternative solutions still hinge much on the proportion of coins.

Since your girl has difficulties on “coins question”, may I suggest you start with concrete objects or picture cut outs for the models. At home, use actual coins for illustration.

Then slowly proceed to using boxes or bars for the MD.

Hope this helps.

Best wishes.

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[tianzhu]

Lynn2:

In the recent exam, she has to do 18 times of guess and check just to get the answer.I think its quite a waste of time tho she eventually gets the answer.

Hi

You don’t really need to use GC for your question as the proportion of coins is given in the question. Solving it by grouping is much more efficient.
However, I’d use it as an illustration to show that a little bit of planning helps to save precious time in using GC.

In this particular question, there are 3 variables, 50 cents coin, 20 cents coin and 10 cents coins.

To get the right combination by getting the guessing randomly is extremely tough.

The question is structured in such a way that you can take away 90 cents (9 10 cents coin) from $11.30.This step is extremely important as it simplifies the solution greatly.

We have 2 times as many 50 cents coin as twenty cents coins. The number of ten cents coin is the same as the number of twenty cents coins after taking away 9.

Now group the ten cents and twenty cents together as a bundle of 30 cents. In this way, we only have two variables 50 cents and the newly formed bundle of 30 cents.

1130 - 90 ----- 1040

So we 1000 + 40 or 900 + 140 or 800 +240 (we are looking for multiples of 30)

240 ----- 8 groups of 30 cents, meaning 8 groups of 20 cents and 10 cents coins which translated into 8 20 cents coins and 17 ten cents coins.
For 800, you’ve 16 50 cents coins.

You need a bit of planning to save time when you use “GC”

Best wishes

[shurley197323]

Pls help. Siti opened a 2kg packet of flour. She used 4/9 of the flour to make a pizza. Then she used 2/7 of the remaining flour to make cakes. Find the mass of the packet of flour that she left. Express answer to 2 decimal place.

Thanks.

[jieheng]

The mass of the packet of flour that she left is


=5/9 * 5/7 * 2

=0.79 kg

[shurley197323]

jieheng:

The mass of the packet of flour that she left is


=5/9 * 5/7 * 2

=0.79 kg

Hi. Thanks. Any working please ?

[jieheng]

5/9 (the mass of flour she left after she use 4/9 for pizza)


5/7 (the mass of flour she left after she use 2/7 for cake)


The mass of the packet of flour that she left is

=5/9 * 5/7 * 2

=0.79 kg

[shurley197323]

Pls help.

1) Ms Lam wants to give some sweets to her pupils. If she gives 7 sweets to each pupil, she will have 380 sweets left. If she gives 15 sweets to each pupils ,she will have 76 sweets left.
(a) How many pupils are there ?
(b) How many sweets does Miss Lam have?

(Not allow to use guess & check methods)

(2) Sue bought an equal no of oranges & pears. Oranges cost 7 for $2 and pears cost 5 for $3. She paid $33 more for pears than oranges.
(a) How much did Sophia pay?
(b) How many oranges and pears did she buy altogether?