Tutor MathsGuru: Ask me for your burning Maths questions!

[Yerdua]

Hi,

These are p1 qns under the "Addition and Subtraction Within 20" topic.
Qns 1: ___ +8-5= 10
Qns 2: ____-7+4=10

Pls advise on how should i teach my ds? Thks thks!

[YLH88]

Hi Vanilla Cake, Dharma,


Thank you so much!!

[MathemathicsPenguin]

sorry, careless..... :oops:

[Vanilla Cake]

MathemathicsPenguin:

Maths Monster:

Can anyone solve this with model?


Given,
p : s = 2 : 5
p : (q + r) = 1 : 3
r : (q + s) = 1 : 2

what is p : q : r : s?

Hi Maths Monster,

Here is the steps and attached model

P:S:Q+R=2:5:6
S+Q:R=1:2
5+6=11
1+2=3
Cross-multiply 11 and 3
S+Q:R=22:11, S:Q+R=15:18
15-11 or 22-18 =4. Q=4.2X3=6=P.
P:Q:R:S = 6:4:11:18.

http://www.postimage.org/image.php?v=aVtHC40

Hi Maths Monster,
Interesting question. Is ratio acceptable to solve instead of model and can I get at least half of the allocated marks for this question? Let's wait patiently for Mathsguru's model solution.


Case 1
p : s
2 : 5

Case 2
p : (q+r)
1 : 3

Case 3
r : (q+s)
1 : 2

Expand case 2 by multiplying by 2 so that \"p\" in case 2 is equivalent to \"p\" in case 1
Expanded Case 2
p : (q+r)
2 : 6

Now, add \"s\" in case 1 and \"(q+r)\" in expanded case 2-> 5+6 = 11.
Note that in case 3, \"r+(q+s)\" = 1+2 = 3.
LCM of 3 and 11 = 33
Since \"s\" in case 1 is 5 and \"(q+r)\" in expanded case 2 is 6, add 5+6= 11.So multiply case 1 and expanded case 2 by 3 to make them equivalent.(11x3=33)
Finally expand case 3 by multiply by 11 so that the new ratio will be added to 33.

Expanded Case 1
p : s
6 : 15

Final Expanded Case 2
p : (q+r)
6 : 18

Expanded Case 3
r : (q+s)
11 : 22

p = 6
r = 11
q = 18-11 = 7
s = 22-7 = 15

p : q : r : s is 6 : 7 : 11 : 15

[Dharma]

Maths Monster:

Can anyone solve this with model?


Given,
p : s = 2 : 5
p : (q + r) = 1 : 3
r : (q + s) = 1 : 2

what is p : q : r : s?

Hi Maths Monster,

This ratio question can be solved easily using ratios as shown by Vanilla Cake. Model method is not required as the qn actually wants you to express the 4 unknowns in one ratio. The qn gives info on 3 diiferent ratios involving 2 or 3 unknowns.

p : s : (q + r) = 2 : 5 : 6
p : (q + r + s )= 2 : 11
r : (q + s) = 1 : 2; so r : (q +r + s) = 1:3
So,
p : (q + r + s) = 6: 33
p : (q + s) : r = 6 : 22 : 11
p : s = 2 : 5 = 6 : 15
p : (q + s) = 6 : (q + 15)

When p = 6; q = 22- 15 = 7; r = 11; s = 15
p:q:r:s = 6:7:11:15

[Dharma]

Yerdua:

Hi,

These are p1 qns under the \"Addition and Subtraction Within 20\" topic.
Qns 1: ___ +8-5= 10
Qns 2: ____-7+4=10

Pls advise on how should i teach my ds? Thks thks!

For this sort of qns, best to work backwards.

For Qn 1

Let’s say we Ali has a certain number of sweets at first. His mother gives him 8 sweets and then he gives 5 sweets to his sister. Ali will have 10 sweets at last.

Now working backwards, Ali would have had 15 sweets (10 + 5) i.e. 5 sweets more, before giving away 5 sweets to his sister.

Before that, Ali will be receive 8 sweets from his mum to have 15 sweets. So, before getting the 8 sweets from his mum, Ali will have 8 sweets less ( 15 – 8= 7) Ali will have 7 sweets at first.

No. of sweets at first = 10 + 5 - 8 = 7

You may wish to try Qn 2.

[Maths Monster]

delete

[Vanilla Cake]

Maths Monster:

Dharma:

[quote=\"Maths Monster\"]Can anyone solve this with model?


Given,
p : s = 2 : 5
p : (q + r) = 1 : 3
r : (q + s) = 1 : 2

what is p : q : r : s?

Hi Maths Monster,

This ratio question can be solved easily using ratios as shown by Vanilla Cake. Model method is not required as the qn actually wants you to express the 4 unknowns in one ratio based on 3 diiferent ratios given involving 2 or 3 unknowns.

p : s : (q + r) = 2 : 5 : 6
p : (q + r + s )= 2 : 11
r : (q + s) = 1 : 2; so r : (q +r + s) = 1:3
So,
p : (q + r + s) = 6: 33
p : (q + s) : r = 6 : 22 : 11
p : s = 2 : 5 = 6 : 15
p : (q + s) = 6 : (q + 15)

When p = 6; q = 22- 15 = 7; r = 11; s = 15
p:q:r:s = 6:7:11:15

Many thanks to Dhama and Vanilla Cake for your answers. The answer is indeed 6:7:11:15.

I agree with you that Ratio method is more appropriate to use than Model for this case. I was stuck when a student asked me for a Model solution. FYI...this is taken from Nanyang 09 Prelim P2 Q12.[/quote]Hi Maths Monster,

You are always welcome!
My younger sister has learnt a lot of new Maths strategies from your posted Maths solutions. Thank you very much for your time and effort.BTW, are you a full time professional specialised top Maths tutor like http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=6311?
Why don't you advertise yourself (I mean tuition service) in this http://www.kiasuparents.com/kiasu/forum/viewforum.php?f=31 of KSP forum so that readers can get to know you better.
My younger sister is VERY weak in using Maths models to solve problem sums and we are VERY worried for her as she is taking PSLE in 2011.My mum may send her for Maths tuition next year when she is in P6.

[Maths Monster]

delete

[Maths Monster]

delete