Q&A - P5 Math

[mathnoobs]

MathIzzzFun:

mathnoobs:

Hi Mathizzfun

Thank you for taking the trouble to draw out a diagram.
I'm afraid I still don't get it.
I've drawn a model here that says Nacho combos costs more than Popcorn combos.
http://i42.tinypic.com/2laa1hj.png\">

can you tell me what is wrong with the diagram ?

Is there a way to tell which is bigger without resorting to diagram ? My child's motor skill is not very good, and has difficulty in getting the relevant boxes to be of the same size.

Hi

The model that you have drawn are of different length which means that the total amount is different.

Note that the total amount of money must be the same ie
total amount of money = (money spent on 4 nachos+3 popcorns) +(money left = 4.50) = (money spent on 3 nachos + 4 popcorns) + (money left = 4.50)

In fact, by noting that there is more money left if I buy 4 nachos and 3 popcorns than if I buy 3 nachos and 4 popcorns means that 3 nachos + 4 popcorns cost more than 4 nacho + 3 popcorn.

http://i40.tinypic.com/n2d1md.jpg\">

cheers.

Hi MathIzzzFun
thank you very much for drawing the diagrams. It is clearer now to see the relationships. Appreciate your time in offering your help. Thank you very again.

[kkme]

Hi MathIzzzFun,


Thanks for your reply.

OMG, I still dont get it.

MathIzzzFun:

kkme:

Hi, need help for these two qns.

1) Tom's present age is thrice Sally's age some years ago. Conversely, Sally's present age is Tom's age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

2) When Kok Hwa's age was twice Bala's age, Mike's age was 30. When Mike's age was twice Kok Hwa's age, Bala was 21. Given that Mike was the oldest among the three persons, find Bala's age when Mike was 62 years old.

Thanks in advance and Happy CNY!

Hi

MD for Q2 which is same as this question that was discussed some time ago - http://www.flickr.com/photos/62167097@N02/5679985631/in/photostream

cheers.

[kkme]

Thks Tianzu!

tianzhu:

kkme:

2) When Kok Hwa's age was twice Bala's age, Mike's age was 30. When Mike's age was twice Kok Hwa's age, Bala was 21. Given that Mike was the oldest among the three persons, find Bala's age when Mike was 62 years old.

Hi

For Q2, due to time constraints, I'll provide some pointers instead of drawing MD.

Case 1
Bala ----- 1 unit
KH ----- 2 units
Mike ------ 30

Difference in age between KH and Bala ----- 1 unit

Difference in age between Mike and KH ----- 30 – 2 units

Case 2
Bala ----- 21
KH ----- 21 + 1 unit
Mike ------ (21 + 1 unit) + (21 + 1 unit)
Difference in age between Mike and KH ----- 21 + 1 unit

Difference in age between two people remains the same.

30 – 2 units ----- 21 + 1 unit

3 units ----- 9
1 unit ----- 3

When Mike’s age was 30, Bala was 3 years old.

62 – 30 ------ 32

Therefore , Bala ----- 3 + 32 ------ 35 years old.

Best wishes

[kkme]

Thks tianzu!

tianzhu:

kkme:

1) Tom's present age is thrice Sally's age some years ago. Conversely, Sally's present age is Tom's age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

Hi

For Q1, you may use MD or Units and Parts.

Due to time constraints, I’ll skip the MD this time.

At present
Tom ----- 3 units
Sally ----- 1 part

Some years ago
Tom ----- 1 part
Sally ----- 1 unit

The difference in age between two people remains the same.

3 units – 1 part ----- 1 part – 1 unit

4 units ----- 2 parts
2 units ----- 1 part

The sum of their present ages is 30 years.

3 units + 2 units ----- 30
5 units ----- 30
1 unit ----- 6

Tom ----- 3 units ----- 18

Best wishes

[mathnoobs]

tianzhu:

kkme:

1) Tom's present age is thrice Sally's age some years ago. Conversely, Sally's present age is Tom's age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

Hi

For Q1, you may use MD or Units and Parts.

Due to time constraints, I’ll skip the MD this time.

At present
Tom ----- 3 units
Sally ----- 1 part

Some years ago
Tom ----- 1 part
Sally ----- 1 unit

The difference in age between two people remains the same.

3 units – 1 part ----- 1 part – 1 unit

4 units ----- 2 parts
2 units ----- 1 part

The sum of their present ages is 30 years.

3 units + 2 units ----- 30
5 units ----- 30
1 unit ----- 6

Tom ----- 3 units ----- 18

Best wishes

Hi Tianzhu
how does one know when to use units and parts ? Here the units are assigned to Sally, and parts to Tom. However, since Tom has age in both present time and some other time, how does one tell whether to assign parts/units based on time or individual ? What is the rational for the assignment ?

[tianzhu]

mathnoobs:

Hi Tianzhu
how does one know when to use units and parts ? Here the units are assigned to Sally, and parts to Tom. However, since Tom has age in both present time and some other time, how does one tell whether to assign parts/units based on time or individual ? What is the rational for the assignment ?

Hi

I am sorry. I can’t answer in detail at this moment.

If you have a copy of Challenging Maths Made Easy, try to do some reading first.

I’ll try to answer your question at a later time.

Best wishes

[usaik]

I need help on the following question : -


K had 64 coins in his coin box. There are 20-cent and 50-cent coins. Total value of all coins was $18.50. How many 20-cent coins and how many 50-cents coins were there?

Appreciate very much your kind help.

[tianzhu]

usaik:

I need help on the following question : -


K had 64 coins in his coin box. There are 20-cent and 50-cent coins. Total value of all coins was $18.50. How many 20-cent coins and how many 50-cents coins were there?

Appreciate very much your kind help.

Hi

You may use “Make a Supposition”

Assume all were 20 cents coins, we’ve 64*20 ------ 1280

Difference between 50cents and 20 cents ------ 30 cents

1850 – 1280 ----- 570
759/30 ------ 19

19 50 cents coins
45 20 cents coins

For more practice, please visit pg 25-27 of this link.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=67&t=25121&start=240

Best wishes

[MathIzzzFun]

usaik:

I need help on the following question : -


K had 64 coins in his coin box. There are 20-cent and 50-cent coins. Total value of all coins was $18.50. How many 20-cent coins and how many 50-cents coins were there?

Appreciate very much your kind help.

Hi

using area model ...

http://i41.tinypic.com/vdnx4y.jpg\">

cheers.

[usaik]

Hi Tianzhu & MathIzzzFun,


Thank you so much for your solution!

Regards.