Tutor MathsGuru: Ask me for your burning Maths questions!

[Awonder]

MathIzzzFun:

Awonder:

Hi, need some help with this problem. TIA.


John is 10 years older than Tommy. In 4 years' time, he will be twice as old as Tommy. How old is John now?

Thanks.

Hi
An important fact to note is AGE DIFFERENCE will ALWAYS remain the SAME.

In 4 years time,
John --> 2 unit
Tommy --> 1 unit
1 unit (age difference) = 10
John --> 20
Tommy --> 10
Now, John --> 20-4 = 16 years old

cheers.

Hi, thanks for yr solution. So are we assuming that Tommy is 10 years old in 4 years time? I still can't reason out myself.

[MathIzzzFun]

Awonder:

MathIzzzFun:

[quote=\"Awonder\"]Hi, need some help with this problem. TIA.


John is 10 years older than Tommy. In 4 years' time, he will be twice as old as Tommy. How old is John now?

Thanks.

Hi
An important fact to note is AGE DIFFERENCE will ALWAYS remain the SAME.

In 4 years time,
John --> 2 unit
Tommy --> 1 unit
1 unit (age difference) = 10
John --> 20
Tommy --> 10
Now, John --> 20-4 = 16 years old

cheers.

Hi, thanks for yr solution. So are we assuming that Tommy is 10 years old in 4 years time? I still can't reason out myself.[/quote]Hi

NOW,
Tommy --> 6 years old
John --> 16 years old

4 years' time,
Tommy --> 6 years + 4 years = 10 years old
John --> 16 years + 4 years = 20 years old
John's age = 2 x Tommy's age

cheers.

[Awonder]

Thanks for your explanation.

[LTQ]

This p6 maths question look simple but how can I get the right answer?


"In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?"

Because the question ask "choose only a mathematics class", to me the answer can be from 0 to 8 students. But the answer from teacher is 20 students. Any wording trick in this question and why 20 students?

Thanks in advance.

[CoffeeCat]

LTQ:

This p6 maths question look simple but how can I get the right answer?


\"In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?\"

Because the question ask \"choose only a mathematics class\", to me the answer can be from 0 to 8 students. But the answer from teacher is 20 students. Any wording trick in this question and why 20 students?

Thanks in advance.

Hmm actually there's something funny, The setter means language = french.
This is a \"standard\" question involving venn diagrams, so maybe you can draw it to visualise the below explanation...
The first sentence implies that any of the 48 students are either in a language (french) class ONLY, a maths class ONLY, or both classes.
(translates to : total no. of students = french only + both + math only
The venn diagram is 2 circle intersecting, 1 circle representing the total number of students in the french class and the other circle representing the total number in math class , and the intersecting region representing the number of students in both classes)

so 7/12 * 48 = 28 students are in the French class, 1/4*48 = 12 students are in both classes. Which means 28-12 = 16 students are not in maths class or in french class ONLY.

Hence the number of students in math class only is 48 - 16 -12 = 20.

[LTQ]

CoffeeCat:

LTQ:

This p6 maths question look simple but how can I get the right answer?


\"In an enrichment class of 48 students, each student must take at least a language class or a mathematics class. 7/12 of the students choose French language and 1/4 of the students choose French language and a mathematics class. How many students choose only a mathematics class?\"

Because the question ask \"choose only a mathematics class\", to me the answer can be from 0 to 8 students. But the answer from teacher is 20 students. Any wording trick in this question and why 20 students?

Thanks in advance.

Hmm actually there's something funny, The setter means language = french.
This is a \"standard\" question involving venn diagrams, so maybe you can draw it to visualise the below explanation...
The first sentence implies that any of the 48 students are either in a language (french) class ONLY, a maths class ONLY, or both classes.
(translates to : total no. of students = french only + both + math only
The venn diagram is 2 circle intersecting, 1 circle representing the total number of students in the french class and the other circle representing the total number in math class , and the intersecting region representing the number of students in both classes)

so 7/12 * 48 = 28 students are in the French class, 1/4*48 = 12 students are in both classes. Which means 28-12 = 16 students are not in maths class or in french class ONLY.

Hence the number of students in math class only is 48 - 16 -12 = 20.

Thank you very much for your explanation.

But like you said, only when language = french then this answer is correct. People can argue that what about those choose English, Chinese... because both \"a language class\" and \"French language\" are mentioned in the question.

If these kinds of unclear question appear in PSLE, wonder how the kids can solve them in a right way...

[lydia_chin]

Hi Maths guru,


pls assist with this question:

There are an equal number of pupils from Class A and Class B at the football field. After a while, half of the pupils from Class A and 42 pupils from Class B left the field and there were 12 more pupils from Class A than Class B remaining at the field.

How many pupils were there at the field at first?

[CoffeeCat]

lydia_chin:

Hi Maths guru,


pls assist with this question:

There are an equal number of pupils from Class A and Class B at the football field. After a while, half of the pupils from Class A and 42 pupils from Class B left the field and there were 12 more pupils from Class A than Class B remaining at the field.

How many pupils were there at the field at first?

Hi,
I presume you will have no problem drawing the models.
Start out by drawing 2 equal bars to represent the number of pupils for class A and B respectively ( 1 above the other for ease of comparison).
Divide the bar for A into 2 equal halves...
From the last information given, after 42 from B left, 1 half of the original bar of A is still 12 more than what's left of B. So 42-12 = 30 is half of the original bar of A. (cut the bar of B such that the cutting line of B is to the left of the cutting line of A).
Hence number of pupils at field at first is 30*2*2 = 120

Arh just saw your post in p3 maths.. hmm they have better model diagram there!

[lydia_chin]

Thanks Coffeecat!

[Herbie]

Factorise 4a^2-b^2-2a-b completely, can help?