Q&A - P3 Math

[corneyAmber]

ck123:

I totally agreed that Maths is not our old time Maths.


My boy bring back HW last week and guess what the questions is not difficult but :shock:

Questions : You are given 2 containers. Capacity of Container A is 4L and Container B is 7L. How can you measure out 5L of water?
It looks more like a logic questions than a maths questions. I have to use 2 containers, goes to the tap, physically pour the water in and out of the containers to show my son. And the last part waas tougher for him \"HOW TO PEN IT DOWN AS ANSWER???????? \"

So we need some language here too........ : :roll:

is this the answer?
pour 7ml water into the 4ml container,
then 3ml left in 7ml container.
then 4ml container pour half away, left 2ml...
pour this 2ml back into 7ml container that contains 3ml to get 5ml.

another way more accurate is:
pour 7ml water into the 4ml container,
then 3ml left in 7ml container.
empty the 4ml container n pour the 3ml into it
mark the 3ml level on the 4ml container
fill 4ml container n pour into 7ml container
fill second time 4ml container n this time pour only water above marking into the 7ml container to make 5ml.

[ck123]

Answer:


First, Pour 4L of water into 7L container.
then fill up 4L container again and pour till 7L container full and so the 4L container would have 1L of water left. Then empty the 7L container and pour the 1L of water from the 4L container to the 7L container. Fill the 4L container again and pour to the 7L container. So now the 7L of container would have 5L of water (1L + 4L).

There is no marking or estimation or half so above is the answer.

See I don't think I can pen it down properly so how to expect my son to do it????

[corneyAmber]

can la...with practice the kids can do it cos it is like a game. sometimes we worry too much.


i just thot of this solution before i read this...cos math is very precise. :lol: but the fun part is in practice we can try 3 different methods n in real life we may need to do that during baking sometimes. thanks for the answer.

[ChiefKiasu]

Yuh… came across the container question before.


Here’s another one from Catholic High. It goes something like this:

Charles and Daniel have the same amount of money. After Charles received twice the amount of money he had and Daniel spent $8, Charles now has 4 times the money Daniel has.

How much did Daniel have at the beginning?

Again… modeling only hor - no cheating with algebra!

[corneyAmber]

ChiefKiasu:

Charles and Daniel have the same amount of money. After Charles received twice the amount of money he had and Daniel spent $8, Charles now has 4 times the money Daniel has.


How much did Daniel have at the beginning?

Again... modeling only hor - no cheating with algebra!

___________
1 unit=u (Charles at first=Daniel at first)

______
u-8 (Daniel spent 8 dollars)

___________ ____________
1u 1u (Charles after it doubles)

______ _____ _____ ______
u-8 u-8 u-8 u-8 (Charles 4 times of Daniel after D spent)

So 4[u-8] = 2u
4u - 32 = 2u
2u = 32
u = 32/2 = 16

So Charles at first = Daniel at first = $16

[David Koriadi]

Hi ChiefKiasu,


This question is from Catholic High School (Primary) P3 CA2 Maths 2007.
Being a newbie,I don't know how to post image in this forum. Anyway the answer is $ 32 via MD method.

Before
Charles U + 8 + U + 8 + U + 8
Daniel U + 8

After
Charles U + U + U + U
Daniel U

4U -> 3U + 24
1U -> 24

Daniel had at the beginning -> U + 8
= 24 + 8
= $ 32 Ans

Is this the correct answer ?

[wwcookie]

ks2me:

1 unit=u (Charles at first=Daniel at first)


______
u-8 (Daniel spent 8 dollars)

___________ ____________
1u 1u (Charles after it doubles)

______ _____ _____ ______
u-8 u-8 u-8 u-8 (Charles 4 times of Daniel after D spent)

So 4[u-8] = 2u
4u - 32 = 2u
2u = 32
u = 32/2 = 16

So Charles at first = Daniel at first = $16

I got the same ans as ks2me :lol: Is this modeling mehod?

[ChiefKiasu]

ks2me:

___________
1 unit=u (Charles at first=Daniel at first)

______
u-8 (Daniel spent 8 dollars)

___________ ____________
1u 1u (Charles after it doubles)

______ _____ _____ ______
u-8 u-8 u-8 u-8 (Charles 4 times of Daniel after D spent)

So 4[u-8] = 2u
4u - 32 = 2u
2u = 32
u = 32/2 = 16

So Charles at first = Daniel at first = $16

Sorry ks2me and wwcookie... both of you fell into the same trap as I when I first did the question. Charles did NOT just DOUBLE his sum of money. He TRIPLED it. Read the question again :).

Also, you were using algebra towards the last step. Naughty naughty

[ChiefKiasu]

David Koriadi:

...This question is from Catholic High School (Primary) P3 CA2 Maths 2007.

Being a newbie,I don't know how to post image in this forum. Anyway the answer is $ 32 via MD method...

Yes... you've got the right answer! But your working still comprise a bit of algebra.

Since I'm lazy to draw, let's say we just let u be the block that represents the sum of money Daniel has after spending $8.

Charles now has 3 times (u+8 )
=> (u+8 )+(u+8 )+(u+8 )
=> u+u+u+8+8+8
=> u+u+u+24

Since Charles also now has 4 times of u, it is clear from the above that u=24.

So Daniel has got u+8 = 24+8 = $32 originally.

[corneyAmber]

wah...the one word \"received\" made so much difference. Actually, to be unambiguous or to highlight, they should put \"received additional\" twice the amount. Hai.... shows that most of us do speed reading... :?