Q&A - P5 Math

[mathnoobs]

MathIzzzFun:

SAHMwith2boys:

Hi, need help with a maths question below:


There was 3 litre 200ml more water in a tank than a pail. After pouring 400 ml of water from the pail to the tank, the amount of water in the tank to the amount of water in the pail became 11:7. How much water was there altogether?

Thanks.

Hi

after pouring 400ml of water from pail to tank, amount of water in the tank would 3200+400+400 = 4000ml more than amount of water in pail.

Amount of water in tank --> 11u
Amount of water in pail --> 7u
4u --> 4000ml, 1u --> 1000ml = 1l
Total amount of water --> 18u = 18 x 1l = 18l

cheers.

I ran this question through my child and he has this question.
If A has 10 apples and B has 5 apples, and B gave A 2 apples, then based on your explanation above, the difference between A and B at the end would be: 5 + 2 + 2 = 9

However, if A has 5 apples and B has 10 apples, and B gave A 2 apples, then the difference would not be 9. The difference would now be 5 - 2 - 2 = 1

The method stated in your solution would work if there is movement from a smaller quantity to a larger quantity.

However, if a question is phrased in such a way that it is unknown whether A or B has the larger quantity, only the difference and the transferred amount was known, how would one solve such a question ?

[linden2000]

mathnoobs:

MathIzzzFun:

[quote=\"SAHMwith2boys\"]Hi, need help with a maths question below:


There was 3 litre 200ml more water in a tank than a pail. After pouring 400 ml of water from the pail to the tank, the amount of water in the tank to the amount of water in the pail became 11:7. How much water was there altogether?

Thanks.

Hi

after pouring 400ml of water from pail to tank, amount of water in the tank would 3200+400+400 = 4000ml more than amount of water in pail.

Amount of water in tank --> 11u
Amount of water in pail --> 7u
4u --> 4000ml, 1u --> 1000ml = 1l
Total amount of water --> 18u = 18 x 1l = 18l

cheers.

I ran this question through my child and he has this question.
If A has 10 apples and B has 5 apples, and B gave A 2 apples, then based on your explanation above, the difference between A and B at the end would be: 5 + 2 + 2 = 9

However, if A has 5 apples and B has 10 apples, and B gave A 2 apples, then the difference would not be 9. The difference would now be 5 - 2 - 2 = 1

The method stated in your solution would work if there is movement from a smaller quantity to a larger quantity.

However, if a question is phrased in such a way that it is unknown whether A or B has the larger quantity, only the difference and the transferred amount was known, how would one solve such a question ?[/quote]Hi. Think this method works whether movement is from smaller or larger quantity container.

For your eg of A having 5 apples and B having 10 apples, the original difference between them is -5 instead of 5 (has to be A-B so as to be like-for-like comparison with first case).

So after the transfer, difference would be -5+2+2 = -1

[mathnoobs]

linden2000:

Hi. Think this method works whether movement is from smaller or larger quantity container.

For your eg of A having 5 apples and B having 10 apples, the original difference between them is -5 instead of 5 (has to be A-B so as to be like-for-like comparison with first case).

So after the transfer, difference would be -5+2+2 = 1

yes, but if the question does not state which has the larger quantity, just the difference between A and B is 5, how would one answer the question ? since one needs to know which has the larger quantity to do a -5+2+2 or a +5+2+2

[MathIzzzFun]

mathnoobs:

MathIzzzFun:

[quote=\"SAHMwith2boys\"]Hi, need help with a maths question below:


There was 3 litre 200ml more water in a tank than a pail. After pouring 400 ml of water from the pail to the tank, the amount of water in the tank to the amount of water in the pail became 11:7. How much water was there altogether?

Thanks.

Hi

after pouring 400ml of water from pail to tank, amount of water in the tank would 3200+400+400 = 4000ml more than amount of water in pail.

Amount of water in tank --> 11u
Amount of water in pail --> 7u
4u --> 4000ml, 1u --> 1000ml = 1l
Total amount of water --> 18u = 18 x 1l = 18l

cheers.

I ran this question through my child and he has this question.
If A has 10 apples and B has 5 apples, and B gave A 2 apples, then based on your explanation above, the difference between A and B at the end would be: 5 + 2 + 2 = 9

However, if A has 5 apples and B has 10 apples, and B gave A 2 apples, then the difference would not be 9. The difference would now be 5 - 2 - 2 = 1

The method stated in your solution would work if there is movement from a smaller quantity to a larger quantity.

However, if a question is phrased in such a way that it is unknown whether A or B has the larger quantity, only the difference and the transferred amount was known, how would one solve such a question ?[/quote]Hi

It will be better if you draw a model to see the transfer.
if A has 5 apples and B has 10 apples, and B gave A 2 apples --> A will have 7 apples and B will have 8 apples. Difference will be 1 apple.

http://i44.tinypic.com/nn7as9.jpg\">


cheers.

[mathnoobs]

MathIzzzFun:

Hi


It will be better if you draw a model to see the transfer.
if A has 5 apples and B has 10 apples, and B gave A 2 apples --> A will have 7 apples and B will have 8 apples. Difference will be 1 apple.

http://i44.tinypic.com/nn7as9.jpg\">


cheers.

Hi MathIzzzFun, you're a very hardworking person. Even on the first day of Chinese New Year, you're answering questions in the morning. I'm very impressed. A Prosperous Chinese New Year to you.

yes, the diagram is very clear. Thank you very much.
I think it would be impossible to answer a question if it is not known from the start if A or B is the larger value.

[MathIzzzFun]

mathnoobs:

MathIzzzFun:

Hi


It will be better if you draw a model to see the transfer.
if A has 5 apples and B has 10 apples, and B gave A 2 apples --> A will have 7 apples and B will have 8 apples. Difference will be 1 apple.

http://i44.tinypic.com/nn7as9.jpg\">


cheers.

Hi MathIzzzFun, you're a very hardworking person. Even on the first day of Chinese New Year, you're answering questions in the morning. I'm very impressed. A Prosperous Chinese New Year to you.

yes, the diagram is very clear. Thank you very much.
I think it would be impossible to answer a question if it is not known from the start if A or B is the larger value.

Hi

it depends on how the question is worded. Usually the relationship of the quantities is either stated upfront or in the end. In the Tank and Pail question, the relationship was clearly stated upfront and in the end - there was more water in the tank and in the end, the amount of water the tank to the amount of water in pail was 11:7.

There is no fixed formula/sequence in tackling such problems if that is what you are looking for. One has to go through the question and then determine the heuristic to solve. For eg. If Alex were to give 2/5 of his stamps to Ben, he would have 6/7 as many stamps as Ben. Find the ratio of Alex's stamps to Ben's stamps.

Happy New Year !

cheers.

[SAHMwith2boys]

MathIzzzFun:

SAHMwith2boys:

Hi, need help with a maths question below:


There was 3 litre 200ml more water in a tank than a pail. After pouring 400 ml of water from the pail to the tank, the amount of water in the tank to the amount of water in the pail became 11:7. How much water was there altogether?

Thanks.

Hi

after pouring 400ml of water from pail to tank, amount of water in the tank would 3200+400+400 = 4000ml more than amount of water in pail.

Amount of water in tank --> 11u
Amount of water in pail --> 7u
4u --> 4000ml, 1u --> 1000ml = 1l
Total amount of water --> 18u = 18 x 1l = 18l

cheers.

Hi MathIzzzFun, thanks for the solution. The ans sheet gave a different ans: 16 litre 200ml. DS had the same solution and ans as what u have stated above, and I wasn't so skillful in Maths to advise him whether his or the ans sheet is right.

Looks like not all ans in ans sheet is right... :xedfingers:

[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!

[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

[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