Mathematics: Post your doubts here!

[salvatore]

if twins are there..confirmed 2 girls
and boys are 6C2

if no twins so u take 5C2 (becuase girls are 7 and minus 2 twins so left 5 )
and that into 6C2 of the boys

therefore 6C2 + 6C2 x 5C2

Thank you for your reply..

I don't get one point here.. if the twins are there, won't the combination be 7C2 (of the girls) X 6C2 (of the boys)?
Why have you omitted the combination of the girls?

 

[syed1995]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Mathematics (9709)/9709_w12_qp_63.pdf
Could anyone please help me with qn no. 6 (a)? I don't understand the marking scheme.
Thanks

PhyZac Dug

finally a stats question...

Total Girls 7
Total Boys 6

2 Boys and 2 girls need to be chosen .. while 2 girls are as such that either they are both in the team or not in the team.

Boys And Twins in Team ( Since there are just 2 team members to be chosen and both will be those 2 twins)
6C2 * 2C2

Boys and Twins Not in Team ( Since there are 7 total girls ... total - 2 twins = 5 girls in total left to choose from)
6C2 * 5C2

Total ways = 165 Ways

 

[PhyZac]

Thank you for your reply..

I don't get one point here.. if the twins are there, won't the combination be 7C2 (of the girls) X 6C2 (of the boys)?
Why have you omitted the combination of the girls?

see what syed1995 wrote.
And I will tell my reply to ur question.

we need 2 girls...and the are 5 normal girls and 2 twin sisters.
If we are to choose the 2 twin sisters. then the girls are confirmed, like there are no more to choose.

If we dont take the twin..we have 5 left...and we take 2 thus 5C2
Hope u get it.

 

[PhyZac]

bro it isnt because its first term ....
when you write the sum it comes ,..... 2 + 4*0.75 +4*0.75^2..... so take 2 out to make "a" same ... it can be 4-2 .... replacing the first 2 by 4 .... and minusing from two...

Sorry, i dint really get you. But i will state my point
Ignore everything for now ,

the answer plainly would have been.
[2(1-0.75^n)/1-0.75]
[8-8(0.75^n)]

And now if you agree to this, next step is to know that the ball travel each step twice, Up and Down so answer will be
[8-8(0.75^n)] x 2
16 - 16(0.75^n)

And now if you agree to this, next step is to know that the first time ball moved down only and not up, so we have to minus 2 meters. Therefore what ever the value 16 - 16(0.75^n) this indicates we have to minus 2 meter

therfore
16 - 16(0.75^n) - 2
14 - 16(o.75^n)

I really hope u get me now.

 

[syed1995]

i can't get why did we do this --> OB = OA + OC

This is a rule... known as a parallelogram rule of vectors..

this is because both the opposite sides of the parallelogram are equal. Like this

a + b = c

 

[GorgeousEyes]

This is a rule... known as a parallelogram rule of vectors..

this is because both the opposite sides of the parallelogram are equal. Like this

a + b = c

Thank youuuu

 

[prekshya]

w-06-qp-6 no. 6 ii help plzz..

 

[syed1995]

sorry but i can't get it

To find number of terms you can do use this formulae. d = (l-a)/(n-1)

You need to keep in mind words like inclusive and non inclusive..

Where d is difference l is last term a is first term and n is total number of terms..

so 5 = (300-100)/n-1
n-1 = 200/5
n-1 = 40
n = 41

 

[PhyZac]

w-06-qp-6 no. 6 ii help plzz..

6 men 3 women
no women beside each other
thus
_M_M_M_M_M_M_
u see, i made blanks between men, and women can choose any of these blanks.
therefore
6! x 7P3 ( 6! because u rearrange the 6 men) (7P3, because out of these 7 blanks, 3 are permutated depeneding on where will 3 women stay)
answer = 151200

 

[syed1995]

w-06-qp-6 no. 6 ii help plzz..

Always link the papers.. people will be able to help you faster...

whenever it asks for not together .. always do Total - Together

Total = 9! = 362880

Two Women Together ..

W W _ _ _ _ _ _
2 women to be chosen out of 3 .. 7 places where these 2 women as a block can be placed .. 6 men + 1 women can go anywhere in the remaining 7 places ..
3P2 * 7 * 7! = 211680

2 Women Not Together = Total - Together
= 9! - 211680
= 151200 Answer

 

[prekshya]

tha

6 men 3 women
no women beside each other
thus
_M_M_M_M_M_M_
u see, i made blanks between men, and women can choose any of these blanks.
therefore
6! x 7P3 ( 6! because u rearrange the 6 men) (7P3, because out of these 7 blanks, 3 are permutated depeneding on where will 3 women stay)
answer = 151200

thanks )

 

[salvatore]

finally a stats question...

Total Girls 7
Total Boys 6

2 Boys and 2 girls need to be chosen .. while 2 girls are as such that either they are both in the team or not in the team.

Boys And Twins in Team ( Since there are just 2 team members to be chosen and both will be those 2 twins)
6C2 * 2C2

Boys and Twins Not in Team ( Since there are 7 total girls ... total - 2 twins = 5 girls in total left to choose from)
6C2 * 5C2

Total ways = 165 Ways

see what syed1995 wrote.
And I will tell my reply to ur question.

we need 2 girls...and the are 5 normal girls and 2 twin sisters.
If we are to choose the 2 twin sisters. then the girls are confirmed, like there are no more to choose.

If we dont take the twin..we have 5 left...and we take 2 thus 5C2
Hope u get it.

I got it now.. thanks a lot guys

 

[GorgeousEyes]

eeeps it waz (300-100)/5 +1
well ummm it said the terms between 300 n 100...thus there r 2oo terms b/t found by subtracting them...n since there is a gap of 5...v divide them by 5....it also said inclusive of 100 n 300...since 300 comes withn tht 200....v ve to add 1 for 100....

i hope u got it...m not much of explainer....

To find number of terms you can do use this formulae. d = (l-a)/(n-1)

You need to keep in mind words like inclusive and non inclusive..

Where d is difference l is last term a is first term and n is total number of terms..

so 5 = (300-100)/n-1
n-1 = 200/5
n-1 = 40
n = 41

Thank you both

 

[falcon678]

Thank you both

pleasure...

 

[prekshya]

s-07-qp-6 no.5ii. help plz..

 

[syed1995]

Thank you both

No Problem!

 

[syed1995]

6 men 3 women
no women beside each other
thus
_M_M_M_M_M_M_
u see, i made blanks between men, and women can choose any of these blanks.
therefore
6! x 7P3 ( 6! because u rearrange the 6 men) (7P3, because out of these 7 blanks, 3 are permutated depeneding on where will 3 women stay)
answer = 151200

Your method seems easier! Thanks for this .. I will be using this from now on

 

[PhyZac]

s-07-qp-6 no.5ii. help plz..

Ok
REFRIGERATOR

now they said 2 Es and no Rs , the word will now be

EFIGEATO

They said, 2 E as compulsory

therefore
EE_ _
and we choose 2 (to make 4 total) from rest letters
FIGATO
6C2 = 15

 

[syed1995]

s-07-qp-6 no.5ii. help plz..

REFRIGERATOR
Total = 12
R =4
E = 2

4 letters to be chosen.. No Rs 2 Es 12-4 = 8

New Data = EEAFIGTO Total = 8

2 E are chosen for sure.. so remaining 6 letters.. AFIGTO

E E _ _

Two letters to be chosen from the remaining 6

= 6C2 * 2C2
= 15 Ways

 

[Rutzaba]

applepie1996

this isnt the ethival way to do it... but still here u are
http://i1275.photobucket.com/albums/y444/Rutzaba/sleep_zpse14b1e9d.png

http://i1275.photobucket.com/albums/y444/Rutzaba/well_zps10150a0f.png