tracywham:

Hi, can i get someone to englighten me in solving this question as in model drawings? Thanks.


Book store A has 40 fewer magazines than book store B. If 130
magazines are transferred from book store B to book store A, there will
be twice as many magazines in book store A as in book store B. How many magazines are there altogether?

hi tracywham,

this is how u draw the model in one (although it might be easier to see if u try to draw 2 models (before and after))
http://i45.tinypic.com/16412p.png\">

from model,
in the end, B will have 1 unit = 90 + 90 + 40 = 220
A will have 2 units = 2 x 220 = 440
Total = 220 + 40 = 660

Nebbermind:

It would be clearer is the sentence had started with

\"Length of A and B WAS...\"

Followed by,
\"Mrs Sim cut...\"

If they want to know the length before cutting, they should ask,
\"What WAS the length of A...\"

If they want to know the new length,
\"What Is the length...\"

Case 2

\"If Mrs Sim cut...\" but in actual fact, she didn't cut. So there is ONLY one length, ie, the original length.

That's just my interpretation. The teacher may not agree.

PS: OK I got what the issue is...original total = 30 or 33cm and so 13cm is possible too...Yes, must ask the teacher the intent of the qn.

I see. If the 30 cm is after cut then the answer is 13 cm.

Anyway your interpretation is correct! Agree wit it!

That's why I said the problem is the question. It was too ambiguous. The original question might be different from what written here.

Nebbermind:

Shouldn't the answer be 9cm? Mrs Sim already cut A (the qn did not say 'If Mrs Sim...').


BTW, the length before cutting is 12cm, not 13cm. 12 cm + 18cm = 30cm.

Any different whether u use IF or not?
Maybe the question is rephrased and some details are gone
so conclusion A at first is 12 cm and in the end is 9 cm.
Anyway why didn't anybody do the working here? haha

Xiao Hu:

Hi Lotto,
Looks like you are assuming the number of bags bought are multiples of 4. Can it not be multiples of 4? If say, number of bags bought is 6, then free pencil case is 2. So he may have bought 1 more pencil case, then ratio of pencil case to bag is 2/6 = 1/3, which is what the end ratio is. But the starting ratio is not 1/4 (1 free pencil case to 6 bags).

I don't know how to solve it in any other way though.

May be gurus like Tianzhu and MathIzzzzFun can help us here?

Thanks,
Xiaohu.

Hi Xiao Hu,

In Maths, our brain is automatically thinking that it must be a multiple of 4 when we read the question (especially for primary school).

If you are looking into that type of answer, u might need to do 4 workings (for multiple of 4, multiple of 4 +1, multiple of 4 +2, multiple of 4 +3) and check one by one and end up with 4 solutions too.

Take it easy! It is not as hard as u think.

Cheers :celebrate:

dazzlego:

lotto:

[quote=\"red rose\"]Hi! Would appreciate help with 2 Trig Qs. Solve:


1. cot(2y+10°)=-0.5

2. 2 sin y + 1 = 3/cosec^2 y

Thanks!

Second question is abit complicated. Please check my work if there is any mistakes.
2 sin y + 1 = 3 sin^2 2y
2 sin y + 1 = 3 sin 2y sin 2y
2 sin y + 1 = 3 (2 sin y cos y) (2 sin y cos y)
2 sin y + 1 = 12 sin^2 y cos^2 y
2 sin y + 1 = 12 sin^2 y (1 - sin^2 y)
2 sin y + 1 = 12 sin^2 y - 12 sin^4 y
12 sin^4 y - 12 sin^2 y + 2 sin y + 1 = 0
Let x= sin y
12 x^4 - 12 x^2 + 2 x + 1 = 0
U can factorize it and get 4 value of x which will lead u to 4 value of y.
I am not sure about it. There must be wrong somewhere. Or maybe we need to try another substitution.

Hi lotto,
You read the question wrongly!
It is 3 / cosec^2 y not 3 / cosec^2 2y

So it would be as simple as this,
2 sin y + 1 = 3 sin^2 y
Let x= sin y
3x^2 - 2x - 1 = 0
(3x + 1) (x - 1) = 0
x = -1/3 or x = 1
sin y = -1/3 or sin y = 1
y = 360 - sin-1(-1/3) or y = 90

Good job! CHeers :celebrate:[/quote]Hi dazzlego,

Thanks for the correction.
I knew it :slapshead:
This carelessness won't leave me alone :frustrated:

red rose:

Hi! Would appreciate help with 2 Trig Qs. Solve:


1. cot(2y+10°)=-0.5

2. 2 sin y + 1 = 3/cosec^2 y

Thanks!

Hi red rose,

First question is quite straight-forward.
First u need to know that tan (2y+10) = -2
since tan is negative, it must be located in IV
2y + 10 = 360 - tan-1(-2)
From here, u can continue yourself
Hope it helps

Second question is abit complicated. Please check my work if there is any mistakes.
2 sin y + 1 = 3 sin^2 2y
2 sin y + 1 = 3 sin 2y sin 2y
2 sin y + 1 = 3 (2 sin y cos y) (2 sin y cos y)
2 sin y + 1 = 12 sin^2 y cos^2 y
2 sin y + 1 = 12 sin^2 y (1 - sin^2 y)
2 sin y + 1 = 12 sin^2 y - 12 sin^4 y
12 sin^4 y - 12 sin^2 y + 2 sin y + 1 = 0
Let x= sin y
12 x^4 - 12 x^2 + 2 x + 1 = 0
U can factorize it and get 4 value of x which will lead u to 4 value of y.
I am not sure about it. There must be wrong somewhere. Or maybe we need to try another substitution.

ozora:

okie i c the error. thanks for highlighting in using parts and units

Or u can times 4 to the ratio in the end since the difference is always the same :evil:

KP2:

lotto:

[quote=\"KP2\"]Need help with Nanyang primary 2011 SA2 paper 2 question no 16.

Hi KP2,

If this is the question that u mean,

[i]Mr Chen bought some pencil cases and bags for the children at a gathering. The price of each pencil case was $2.40 while the price of each bag was $10.80. For every 4 bags bought, he was given one such pencil case for free. After receiving the free pencil cases, the number of pencil cases was 1/3 of the number of bags bought.
If Mr Chen paid a total of $1584, how much more did he pay for the bags
than the pencil

The answer key is wrong I think :scratchhead:
Hope mine is correct and can be understood.
But it is way too messy :imsorry:
I'm still not use to post solution here

Thx Lotto ! Ur answer is the same as the answer key .[/quote]


Your welcome.
Why is mine wrong... Grrr :mad:

jedamum:

lotto:

Math is not all about counting. There are a lot of things in this world that can be related to maths.

In my opinion, it would be so much more enjoyable for our DC if we guide them ourselves in the early age than we send them to e centre.

i coach ds1 in math. to him, it is all about drill.
i send ds2 to math e centre. to him, math is all about games.
i think it is about attitude towards math. it is not about too teach.
if i had engaged a fun attutide when teaching ds1, he would have think that math is fun. if the math e centre that ds2 goes to focus on drilling, he would think it is about drilling.

Seems like our ds1 and ds2 is the same.
ds1 is always train himself in math and won a lot of medals and ds2 is happy go lucky type.
I stopped coaching them at the same time (bcoz of work) until ds1 p4 and ds2 p3 (since ds1 is 1 year older)
maybe I didn't gave enough to ds2 (compare to ds1), so ds2 score is abit low.
Then ds2 always said it's all happened because i trained him 1 year less then his kor. i kind of :sad: when i heard that.
Coz i love both of them equally :grphug:

Sorry it's kinda of off topic alr :oops:

ozora:

verykiasumummy:

[quote=\"ozora\"]Need guide in this question only: The number of basketballs was 3/5 of the number of footballs. In jan , 1/3 of the basketball and 1/3 of the football were sold. In feb,4 basketball n 4 footballs were sold. The number of basketballs left was 1/2 of the number of footballs. How many basketballs were there at first?


Thanks

just trying to help.

The number of basketballs was 3/5 of the number of footballs.

means ratio of basket:foot is 3:5.

In jan , 1/3 of the basketball and 1/3 of the football were sold.

so ratio has to be multiplied by 3.
basket : foot
9 : 15
-3u -5u
---------------
6 : 10

In feb,4 basketball n 4 footballs were sold.

basket : foot
6 : 10
-4 -4
---------------
1 : 2

since 6u-2u=4u, and 10u-2u=8u, which is exactly half, therefore

2u --> 4
1u --> 2
at first there were 9u basketball, so
9u --> 18

ans is 18.

think there is a mistake. the subtraction of basket is 6u-1u =5u .
therefore cannot be half.[/quote]
@ozora:
try to use units and parts to continue from the table given! u can find that 2u = 4

@verykiasumummy:
your steps to get '2u = 4' is not so reliable. if the number is not so nice, u might not be able to guess the '2u'
Nice one btw :celebrate: