Tutor MathsGuru: Ask me for your burning Maths questions!

[YLH88]

Hi Mathsguru,


Need your help with the following questions : :?:

1) At first, there were 230 kg of oranges and durians in a market. After 60% of the oranges and 20 kg of the durians were sold, the remaining oranges and durians were of equal weight. What was the original weight of the durians ?

2) There are 480 people in Group X and 20% of them are children. There were 380 people in Group Y and 70% of them are children. After some people were transferred from Group Y to X, 40% of the people in Group X and 50% of the people in Group Y are children. How many people are transferred from Group Y to Group X ?

3) Mrs Winder had some $50 notes and $10 notes. The number of $50 notes is 45% that of $10 notes. She spent 20% of the $50 notes. As a result, she had 192 more $10 notes than $50 notes.
(a) What was the amount of money spent ?
(b) Express the amount of $10 notes as a fraction of the amount of $50 notes left.


Thank you very help !

[worldangel]

CoffeeCat:

Yea I mean 6.67 by itself is asking to be marked wrong.

Hmm...care to elaborate what you mean? She did all the working but instead of writing the final answer as Ans: 6 2/3, she wrote it as Ans: 6.67...


Of course before that final answer, all the working and steps were shown clearly. Just that instead of using mixed number, she used decimal...so the final answer was left as a decimal. So she lost the one mark for the answer because the teacher claimed it should be left as mixed number, not decimal. But that was not stated in the question...that's why we were wondering why the final answer in decimal is not accepted.

Thanks in advance again.

[CoffeeCat]

worldangel:

Hmm...care to elaborate what you mean? She did all the working but instead of writing the final answer as Ans: 6 2/3, she wrote it as Ans: 6.67...



Of course before that final answer, all the working and steps were shown clearly. Just that instead of using mixed number, she used decimal...so the final answer was left as a decimal. So she lost the one mark for the answer because the teacher claimed it should be left as mixed number, not decimal. But that was not stated in the question...that's why we were wondering why the final answer in decimal is not accepted.

Thanks in advance again.

oh ok you see, 6.67 is not the same quantity as 6.66666...
That is why if you write 6.67 (correct to 2 d.p), then there is a fighting chance to get the marks.

[CoffeeCat]

YLH88:

Hi Mathsguru,


Need your help with the following questions : :?:

1) At first, there were 230 kg of oranges and durians in a market. After 60% of the oranges and 20 kg of the durians were sold, the remaining oranges and durians were of equal weight. What was the original weight of the durians ?

2) There are 480 people in Group X and 20% of them are children. There were 380 people in Group Y and 70% of them are children. After some people were transferred from Group Y to X, 40% of the people in Group X and 50% of the people in Group Y are children. How many people are transferred from Group Y to Group X ?


3) Mrs Winder had some $50 notes and $10 notes. The number of $50 notes is 45% that of $10 notes. She spent 20% of the $50 notes. As a result, she had 192 more $10 notes than $50 notes.
(a) What was the amount of money spent ?
(b) Express the amount of $10 notes as a fraction of the amount of $50 notes left.


Thank you very help !

I am not mathsguru but...
1)Weight of 60% of oranges + 40% oranges + 40%oranges = 230-20=210.
Weight of 40% oranges = 210 * 40 % / 140% = 60kg
weight of durians = 60 + 20 = 80kg

What level is this from anyway?

2)Number of children in X = 20% * 480 = 96
Number of adults in X = 384
Number of children in Y = 70% * 380 = 266
Number of adults in Y = 114

After the transfer...
40% of X + 50% Y = 96 + 266 = 362 children
60 % of X + 50% of Y = 384 + 114 = 498 adults
20% of X = 498 - 362 = 136
X = 136 * 5= 680
Number of ppl transfered = 680 - 480 = 200
(Key is that the total number of children and adults is constant)

3)
a)Number of $50 notes is 45% of $10 notes
After spending 20% of the $50 notes, the number of $50 notes left is (80% * 45%) = 36% of $10 notes
192 = (100-36= 64)% of $10 notes
Amount of money spent = (192/ 64%) * (45%-36%) = $27

b) Ans = reciprocal of 36% = 100/36 = 25/9

My workings might not be very clear. The real Mathsguru will probably give you a better form.

[worldangel]

CoffeeCat:

oh ok you see, 6.67 is not the same quantity as 6.66666...

That is why if you write 6.67 (correct to 2 d.p), then there is a fighting chance to get the marks.

I see...think next time I will just tell them to leave answer as mixed number unless the question asks for decimal...

thanks for the clarification!

[david59]

worldangel:

CoffeeCat:

Yea I mean 6.67 by itself is asking to be marked wrong.

Hmm...care to elaborate what you mean? She did all the working but instead of writing the final answer as Ans: 6 2/3, she wrote it as Ans: 6.67...


Of course before that final answer, all the working and steps were shown clearly. Just that instead of using mixed number, she used decimal...so the final answer was left as a decimal. So she lost the one mark for the answer because the teacher claimed it should be left as mixed number, not decimal. But that was not stated in the question...that's why we were wondering why the final answer in decimal is not accepted.

Thanks in advance again.

In Maths, certain expectations are expected when instruction is not given. For eg. an answer on fraction must be in its lowest form even if no instruction is given.
So, if the answers end with one third or two third, unless there is instruction that the answer be given up to say 2 or 3 decimal places, the answer should end with the 1/3 or 2/3 which are exact values. Giving an answer like .67 or .33 is really an approximate answer, though very close to the exact value.
Hope my explanation helps.

[small]

YLH88:

Hi Mathsguru,


Need your help with the following questions : :?:

1) At first, there were 230 kg of oranges and durians in a market. After 60% of the oranges and 20 kg of the durians were sold, the remaining oranges and durians were of equal weight. What was the original weight of the durians ?

2) There are 480 people in Group X and 20% of them are children. There were 380 people in Group Y and 70% of them are children. After some people were transferred from Group Y to X, 40% of the people in Group X and 50% of the people in Group Y are children. How many people are transferred from Group Y to Group X ?

3) Mrs Winder had some $50 notes and $10 notes. The number of $50 notes is 45% that of $10 notes. She spent 20% of the $50 notes. As a result, she had 192 more $10 notes than $50 notes.
(a) What was the amount of money spent ?
(b) Express the amount of $10 notes as a fraction of the amount of $50 notes left.

Thank you very help !

Hi HLY88,

Hope this helps. (Only for question 1 and 3 as I still trying on question 2)

http://www.postimage.org/image.php?v=aV3ZIWr

http://www.postimage.org/image.php?v=gxuS7Kr

[mathsguru]

chiclil:

Hi Mathsguru

Sorry but this is just P2 maths question but I am not sure how to present the workings.

Question 1.
Cheryl and David work in the same building.
Cheryl is on the 18th floor.
David is on the 29th floor.
How many floors are in between them ?
( I would actually just count from 19 to 28 th floor as answer 10 but not sure if there is a proper way to present the answer)

Question 2
Study the pattern and put in the missing number.
What should the answer be ?
http://www.postimage.org/

Hi Chiclil,

Here're my solutions with some explanation and tips. Hope they can aid you when you teach your child.

Cheers,
MathsGuru

http://www.postimage.org/image.php?v=aV5PYhS

http://www.postimage.org/image.php?v=aV5PVNJ

[mathsguru]

worldangel:

I have a question here:


If the question never states to leave the answer as fraction/mixed number or decimal, can the child leave the answer as a decimal and still get it correct?

For example, the child writes the answer as 6.66667 = 6.67. The answer is
6 2/3.

This is for a question in Paper 2 btw. Thanks in advance

Hi WorldAngel,

If the question never states, I usually encourage my students to leave as a mixed number or fraction. Decimal numbers are ok only when they are terminating decimal (i.e. non-recurring like 6.6 not 6.6666666666666....).

There's a S<-->D function in the calculator that can easily convert decimal numbers to fraction (vice-versa) which is quite useful.

If the question states \"leave your answer in decimal\" but the answer is a recurring decimal, round off to 2 or 3 decimal places and state that in the working. Usually if the question has answer like that, the question will state the no. of decimal places e.g. \"round your answer off to 2 decimal places\".

Hope this clarifies!

Cheers,
MathsGuru

[mathsguru]

YLH88:

Hi Mathsguru,


Need your help with the following questions : :?:

1) At first, there were 230 kg of oranges and durians in a market. After 60% of the oranges and 20 kg of the durians were sold, the remaining oranges and durians were of equal weight. What was the original weight of the durians ?

2) There are 480 people in Group X and 20% of them are children. There were 380 people in Group Y and 70% of them are children. After some people were transferred from Group Y to X, 40% of the people in Group X and 50% of the people in Group Y are children. How many people are transferred from Group Y to Group X ?

3) Mrs Winder had some $50 notes and $10 notes. The number of $50 notes is 45% that of $10 notes. She spent 20% of the $50 notes. As a result, she had 192 more $10 notes than $50 notes.
(a) What was the amount of money spent ?
(b) Express the amount of $10 notes as a fraction of the amount of $50 notes left.


Thank you very help !

Hi YLH88,

Here are my solutions. Hope you find them useful!

Cheers,
MathsGuru

http://www.postimage.org/image.php?v=aV5ThOS

http://www.postimage.org/image.php?v=aV5TmO9

http://www.postimage.org/image.php?v=aV5TfjJ