O-Level Additional Math

[pinkapple]

yup.

[mum_sugoku]

Eddow:

oh.. you're assuming +9(x^ab) - 81. And I'm assuming -9(x^ab) +81, that's why ans diff.


It's just printing error in the original question.

Agree with you - I also tried a few \"+\" & \"-\" combinations, but none can give answer that matches the question exactly :scratchhead:

[wkong]

Hi I have two questions from my son:


1. Find the smallest whole number that is not a factor of 12345…31

2. Find the largest prime number that divides this number

123…59+123*4…*60

Thank you in advance.

[FrekiWang]

wkong:

Hi I have two questions from my son:


1. Find the smallest whole number that is not a factor of 1*2*3*4*5......*31

2. Find the largest prime number that divides this number

1*2*3....*59+1*2*3*4.....*60

Thank you in advance.

1. 37
2. 61

I have to say that your son's trainer (most probably maths olympiad) is a failure >_< as these are very simple questions at competition level.

[wkong]

FrekiWang:

wkong:

Hi I have two questions from my son:


1. Find the smallest whole number that is not a factor of 1*2*3*4*5......*31

2. Find the largest prime number that divides this number

1*2*3....*59+1*2*3*4.....*60

Thank you in advance.

1. 37
2. 61

I have to say that your son's trainer (most probably maths olympiad) is a failure >_< as these are very simple questions at competition level.

Thanks Freki for your help. My DS wasn't trained for maths olympiad. This is part of his sch maths homework given by his sch teacher.

[Herbie]

I hv 2Qn.


1 factorise 3x^2+26x+51.
HENCE OR OTHERWISE FIND TWO FACTORS OF 32651.

2. If (a+b)^2=73 and ab=6.5, CALCULATE THE VALUE OF a^2+b^2

Can help to show the working? Tq

[mum_sugoku]

Herbie:

I hv 2Qn.


1 factorise 3x^2+26x+51.
HENCE OR OTHERWISE FIND TWO FACTORS OF 32651.

2. If (a+b)^2=73 and ab=6.5, CALCULATE THE VALUE OF a^2+b^2

Can help to show the working? Tq

1. (3x^2+26x+51) = (3x+17)(x+3)

32651=3*100^2 +26*100 +51 ==> x=100

Hence factors are (3*100+17) ie 317, and (100+3) ie 103.

2. (a+b)^2=a^2+2ab+b^2

==> 73 = a^2 + 2(6.5) +b^2
hence a^2 + b^2 =73 - 2(6.5) = 60

[Xiao Hu]

Hi FrekiWang,


Need help on this question, I think it’s 2010 O level Maths paper 1 question.
Part2 looks innocuously easy, but it trips me up. Difficult to put my reasonings in writings.

There are 2 parts to the question.
#1. Factorise 90. This is easy, 90=2x3x3x5

#2
LCM of 6,15 and x is 90. What are possible values of x if x is odd?

From #1, since 90=6x15, how can this be used to work out possible values of x?

The answers given for x are 9 and 45.

TIA,
Xiao Hu.

[FrekiWang]

Xiao Hu:

Hi FrekiWang,


Need help on this question, I think it's 2010 O level Maths paper 1 question.
Part2 looks innocuously easy, but it trips me up. Difficult to put my reasonings in writings.

There are 2 parts to the question.
#1. Factorise 90. This is easy, 90=2x3x3x5

#2
LCM of 6,15 and x is 90. What are possible values of x if x is odd?

From #1, since 90=6x15, how can this be used to work out possible values of x?

The answers given for x are 9 and 45.

TIA,
Xiao Hu.

90=2*3^2*5
6=2*3
15=3*5
Therefore, x=2^a * 3^2 * 5^b
where a=0 or 1(reject as odd) and b=0 or 1
when a=0,b=0: x=3^2=9
when a=0,b=1: x=3^2*5^1=45

[Xiao Hu]

FrekiWang:

Xiao Hu:

Hi FrekiWang,


Need help on this question, I think it's 2010 O level Maths paper 1 question.
Part2 looks innocuously easy, but it trips me up. Difficult to put my reasonings in writings.

There are 2 parts to the question.
#1. Factorise 90. This is easy, 90=2x3x3x5

#2
LCM of 6,15 and x is 90. What are possible values of x if x is odd?

From #1, since 90=6x15, how can this be used to work out possible values of x?

The answers given for x are 9 and 45.

TIA,
Xiao Hu.

90=2*3^2*5
6=2*3
15=3*5
Therefore, x=2^a * 3^2 * 5^b
where a=0 or 1(reject as odd) and b=0 or 1
when a=0,b=0: x=3^2=9
when a=0,b=1: x=3^2*5^1=45

Hi FrekiWang,
Good one!! I could't have expessed the solution this way, I would have them in English.
This is a bit tough for O level Maths, isn't it? It's only 1 mark. Crazy.

Thanks very much, appreciate it.
Xiao Hu.