Q&A - P3 Math

[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... :?

[wwcookie]

ChiefKiasu:

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

Oh ya dint read the question properly :oops:

[ChiefKiasu]

wwcookie:

Oh ya dint read the question properly :oops:

Actually, this highlights the importance of English for our children in Primary schools. Without a good foundation in English, it will affect their performance in other subjects such as Math and Science. It is no wonder that parents these days are focusing so much in building up their pre-school children's English competency before Primary 1.

[mckenzy]

ChiefKiasu:

David Koriadi:

...


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.

i don't understand how you conclude that u = 24

teach me!!! :oops:

[ChiefKiasu]

mckenzy:

i don't understand how you conclude that u = 24


teach me!!! :oops:

Here's another way of looking at it.
Let u = what Daniel has after he spent $8
So u+8 is what Daniel has before he spent $8
3 times of (u+8 ) is equal to 4 times of u
=> 3u + 24 = 4u
=> u = 24

[mckenzy]

okay when i read your post last night i still didn’t get it… this morning a little better…


thanks!

[Priskhipo]

mckenzy:

okay when i read your post last night i still didn't get it... this morning a little better...


thanks!

Hi,
Hope the model drawing illustrates the solution better.


http://www.postimage.org/image.php?v=gxPOgw9

[ChiefKiasu]

Priskhipo:

Hi,

Hope the model drawing illustrates the solution better...

Thanks Priskhipo! Crystal clear now.