O-Level Additional Math

[benorito]

Hi,


Can you kindly help with this question :
Given that 280 and a number y have a LCM of 6160 and a HCF of 40, find the number y.

Thanks in advance!

[iFruit]

benorito:

Hi,


Can you kindly help with this question :
Given that 280 and a number y have a LCM of 6160 and a HCF of 40, find the number y.

Thanks in advance!

You need to know that product of two numbers = HCF x LCM of those two numbers


280 * y = 6160 * 40

y = (6160 * 40)/280 = 880

[benorito]

iFruit:

You need to know that product of two numbers = HCF x LCM of those two numbers


280 * y = 6160 * 40

y = (6160 * 40)/280 = 880

Thank you !!

[SKT]

Hi,

Given that x and y satisfy the simultaneous equations
mx + (m-1)y = 10,
(m-2)x + 3my = 20.

(a) If the equations have no unique solution, find the values of m.
(b) If the equations have no solutions, find the value of m.

TIA.

[iFruit]

SKT:

Hi,

Given that x and y satisfy the simultaneous equations
mx + (m-1)y = 10,
(m-2)x + 3my = 20.

(a) If the equations have no unique solution, find the values of m.
(b) If the equations have no solutions, find the value of m.

TIA.

Using Cramer’s rule

x = [30m - 20(m-1)]/ [3m² – (m² -3m +2)] = (10m+20)/ (2m² + 3m -2)

y = [20m -10(m-2)] / (2m² + 3m -2) = (10m+20)/ (2m² + 3m -2)


Recall that equation has
1) infinite solutions when (10m+20) = 0 and (2m²+ 3m -2)=0
2) No solutions when (10m+20) # 0 and (2m² + 3m -2)=0

(2m² + 3m -2)= (2m-1)(m+2) =0----> m=-2 or m=1/2


When m=-2, 10m+20 = 0,
when m=1/2, 10m+20 = 25


So infinite solutions when m=-2
No solutions when m=1/2

[atutor2001]

SKT:

Hi,

Given that x and y satisfy the simultaneous equations
mx + (m-1)y = 10,
(m-2)x + 3my = 20.

(a) If the equations have no unique solution, find the values of m.
(b) If the equations have no solutions, find the value of m.

TIA.

Below is an ELEMENTARY approach

For linear equation : y = mx +c

(a) 2 lines will have no unique solution if they are the same line i.e. both lines have the same gradient, m and the same y-intercept, c

mx + (m-1)y = 10 that is: y = -mx/(m-1) +10/(m-1)
(m-2)x + 3my = 20 that is: y = -(m-2)/(3m) + 20/(3m)

If the gradients are the same :

-mx/(m-1) = -(m-2)/(3m)
3m² = m²-2m-m+2
2m²+3m-2 = 0
(2m-1)(m+2) = 0
m = 1/2 or -2

If the y-intercepts are the same :

10/(m-1) = 20/(3m)
30m = 20m - 20
m = -2

Therefore, there is no unique solution if m = -2

(b) 2 lines will have no solution if they are parallel i.e. same gradient but different y-intercept.

Therefore, there is no solution if m = 1/2

[SKT]

Hi,


However, the answer provided for (a) is 1/2, -2, wonder what's the meaning of \"no unique solution\". Are the two lines parallel or collinear or both?

TIA

[iFruit]

SKT:

Hi,


However, the answer provided for (a) is 1/2, -2, wonder what's the meaning of \"no unique solution\". Are the two lines parallel or collinear or both?

TIA

That is right.

No Unique solution means, either no solution or infinite solutions.

when m=-2, there are infinite solutions (when it's the same line)

so both 1/2 and -2 are answers for (a).

[atutor2001]

SKT:

Hi,


However, the answer provided for (a) is 1/2, -2, wonder what's the meaning of \"no unique solution\". Are the two lines parallel or collinear or both?

TIA

NO UNIQUE solution means these 2 lines are collinear (2 lines overlapping each other, so every point on the lines is a solution or can say there are infinite number of solutions)
So answer for (a) is -2 ONLY

NO solution means these 2 lines are parallel but NOT collinear (these 2 lines will never meet which is why there is no solution)
So answer for (b) is 1/2

[iFruit]

atutor2001:

SKT:

Hi,


However, the answer provided for (a) is 1/2, -2, wonder what's the meaning of \"no unique solution\". Are the two lines parallel or collinear or both?

TIA

NO UNIQUE solution means these 2 lines are collinear (2 lines overlapping each other, so every point on the lines is a solution or can say there are infinite number of solutions)
So answer for (a) is -2 ONLY

NO solution means these 2 lines are parallel but NOT collinear (these 2 lines will never meet which is why there is no solution)
So answer for (b) is 1/2

A system of linear equations will have one of the three possible types of solutions

1) Unique solution
2) Infinite solutions
3) no solution

when you say \"no unique solution\" (the opposite of 1 in the list ) it should cover the cases of both 2 and 3 above.

so for (a) in the question, both 1/2 and -2 are the answers, IMHO.