Mei Ping
Asked 9 years ago

SG chevron_right Primary 5 chevron_right Measurement

Pls kindly help this P5 math.I don't understand it.Thanks in advance.

Replies 2
Raymond Ng

6 years ago
Mei Ping

I got it,very clear.πŸ‘πŸΏπŸ‘πŸΏ many thanks Raymond.

6 years ago

Adrian Ng
Asked 9 years ago

SG chevron_right Primary 6 chevron_right Number and Algebra

Making it visual...

Replies 1
Adrian Ng

Shirley Goh

6 years ago

James Zheng
Asked 9 years ago

SG chevron_right Secondary 4 chevron_right Add Math: Geometry and Trigonometry

Can anyone please help to solve this sec. 4 maths question? Thank you in advance.

Replies 8
Raymond Ng

6 years ago
Winnie Win

Is this A Maths or E Maths?

6 years ago
James Zheng

A math

6 years ago
Winnie Win

I see. Thanks

6 years ago
James Zheng

Thank you Raymond Ng

6 years ago
Raymond Ng

This paper is from which country?

6 years ago
James Zheng

Raymond Ng: It is from Singapore

6 years ago
Raymond Ng

Ok... coz I saw the unit used was "ft"... so I guess it's from IGCSE or the like

6 years ago
Raymond Ng

This paper is from which country?

6 years ago
Winnie Win

I see. Thanks

6 years ago
James Zheng

Raymond Ng: It is from Singapore

6 years ago
Raymond Ng

Ok... coz I saw the unit used was "ft"... so I guess it's from IGCSE or the like

6 years ago

Adrian Ng
Asked 9 years ago

SG chevron_right Primary 5 chevron_right Number and Algebra

Making it visual...

Replies 0

Mei Ping
Asked 9 years ago

SG chevron_right Primary 5 chevron_right Number and Algebra

Kindly help,thanks in advance .

Replies 7
Raymond Ng

6 years ago
Mei Ping

Raymond,can u pls share how u got the idea to solve this question ? Its so easy but I didn't even think of it 😩！

6 years ago
Raymond Ng

Hi Mei Ping This is known as the complement method (or in layman's term, "back door" approach). Firstly, I imagine all the points are joined to every other points i.e. the "boundary" of the shape is included. There are n sides. Calculating this is not difficult. This is similar to a common kind of question which goes like this: "There are n people in a party. If everyone shakes hands with everybody else, how many handshakes are there in total?" Each person will shake hands with (n-1) people. So all n of them will do that. At first glance, total handshakes = n(n-1). On closer scrutiny, you should realise that you have double counted every handshake. (Think: A shakes hand with B and B shakes hand with A refer to the same handshake!) Realising this fact, we can either use n(n-1) Γ· 2 to get the answer or simply count as follows: 1+2+3+...+n-1 which gives the same answer. Then, we must minus the n we had added to simplify the problem. Hope this helps. P.S. Actually, if we use algebra to simply & generalise the expression, you will get (1+2+3+...+n-1) - n = n(n-1) Γ· 2 - n = n(n-3) Γ· 2

6 years ago
Raymond Ng

Alternatively, if you prefer a direct approach, think of it this way: Every person (point) can shake hand with everyone at the party (diagram) except for itself & it's left and right neighbours. So if there are n persons (points) there are (n-3) handshakes per person. Total = n(n-3) handshakes (lines). However, due to double counting (as explained above), answer = n(n-3) Γ·2

6 years ago
Mei Ping

Thanks very much Raymond πŸ‘πŸ‘πŸ‘

6 years ago
Ana Neves

(n x (n - 3)) : 2

6 years ago
Mei Ping

Thanks Raymond n Ana πŸ‘

6 years ago
Mei Ping

Raymond,can u pls share how u got the idea to solve this question ? Its so easy but I didn't even think of it 😩！

6 years ago
Raymond Ng

Hi Mei Ping This is known as the complement method (or in layman's term, "back door" approach). Firstly, I imagine all the points are joined to every other points i.e. the "boundary" of the shape is included. There are n sides. Calculating this is not difficult. This is similar to a common kind of question which goes like this: "There are n people in a party. If everyone shakes hands with everybody else, how many handshakes are there in total?" Each person will shake hands with (n-1) people. So all n of them will do that. At first glance, total handshakes = n(n-1). On closer scrutiny, you should realise that you have double counted every handshake. (Think: A shakes hand with B and B shakes hand with A refer to the same handshake!) Realising this fact, we can either use n(n-1) Γ· 2 to get the answer or simply count as follows: 1+2+3+...+n-1 which gives the same answer. Then, we must minus the n we had added to simplify the problem. Hope this helps. P.S. Actually, if we use algebra to simply & generalise the expression, you will get (1+2+3+...+n-1) - n = n(n-1) Γ· 2 - n = n(n-3) Γ· 2

6 years ago
Raymond Ng

Alternatively, if you prefer a direct approach, think of it this way: Every person (point) can shake hand with everyone at the party (diagram) except for itself & it's left and right neighbours. So if there are n persons (points) there are (n-3) handshakes per person. Total = n(n-3) handshakes (lines). However, due to double counting (as explained above), answer = n(n-3) Γ·2

6 years ago
Mei Ping

Thanks very much Raymond πŸ‘πŸ‘πŸ‘

6 years ago

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