Homework Assistance Please? (Maths)

basilmarket.com forums : Chat | 15 posts archived

thread starter benniu Oct 25 2010 + PM | QUOTE | PERMALINK | REPORT

I have maths work to do and i can't do a few hard questions can anyone help me? (By the way these questions are on Quadratics) Q1) A bag contains 3 red balls and w white balls. Maggie draws two balls together from the bag. The probability that they have the same colour (Australian Spelling =D) is 1/2. Bill adopts a different procedure. He draws one ball from the bag notes its colour and replaces it. He then draws a second ball from the bag and notes its colour. The probability that both balls have the same colour is now 5/8. Find all possible values of w . Q2)A rhombus has half the area of a square with the same side-length, the ratio of the long to short diagonal is: (A) 2+ root3 (B) 2-root3 (C) 1/2 (D) 2 (E) root3 Q3) Form a pair of simultaneous equations and solve them to x and y , given that they are rational: xy + root3= 10+root x-y Thanks (Sorry i couldnt add the root sign coz the site wouldn't let me

My Characters: ShiftySteve - 35 Bera Blade Acolyte

realmdefendr 10/25/10 + PM | QUOTE | PERMALINK | REPORT

The only one I can do is Q3, sadly, considering I have a HSC maths exam on Wednesday . In this question, xy = 10 , root(x - y) = root(3), and so therefore (x - y) = 3. Then, from that, y = x - 3 and use simultaneous equations, subbing in this to xy = 10. I think you'll get x = 5, -2; and then you find both values of y. If that makes sense.

My Characters: realmdefendr - 65 Scania Hunter

SilentXynh 10/25/10 + PM | QUOTE | PERMALINK | REPORT

@TS: For Q1, do we assume Maggie draws a ball one at a time? realmdefendr Good luck for 3U :P I have a few friends stressing about 3U, seeing as they have an exam tomorrow as well xD Ahh, the joys of not having to go through the HSC again

My Characters: Aussenritter - 90 Scania Dawn Warrior

benniu + PM | QUOTE | PERMALINK | REPORT

[quote] realmdefendr : The only one I can do is Q3, sadly, considering I have a HSC maths exam on Wednesday . In this question, xy = 10 , root(x - y) = root(3), and so therefore (x - y) = 3. Then, from that, y = x - 3 and use simultaneous equations, subbing in this to xy = 10. I think you'll get x = 5, -2; and then you find both values of y. If that makes sense. [/quote] Haha surprisingly the first question is from a HSC past paper, tsk tsk you should know this =D @ above- Sorry i dont know D= the question doesn't say.

My Characters: ShiftySteve - 35 Bera Blade Acolyte

SilentXynh + PM | QUOTE | PERMALINK | REPORT

I'm having more problem with the probability more than anything else @_@ I got part of the answer for q1, still trying to work out how the first part ties in with it. With the second person's method: Total number of balls = 3+w Probability of getting red then red = [3/(3+w)]^2 Probability of getting white then white = [w/(3+w)]^2 Probability of getting the same colour is the sum of those [3/(3+w)]^2 + [w/(3+w)]^2 = 5/8 Simplify, expand, etc You get: w^2 - 10w + 9 = 0 (w-9)(w-1) = 0 First method: Probability of getting the same colour = 1/2 = probability of getting different colour (as the probability must add up to 1) Probability of getting red then white = [3/(3+w)]*[w/(2+w)] Probability of getting white then red = [w/(3+w)]*[3/(2+w)] So the probability of getting a different colour is the sum of those two. But they're in fact equal, so: 2*[3/(3+w)]*[w/(2+w)] = 1/2 Expand and simplify Brings you down to: w^2 - 7w + 6 = 0 (w-6)(w-1) I believe the answer would be w = 1, as it must agree with both methods.

My Characters: Aussenritter - 90 Scania Dawn Warrior

realmdefendr + PM | QUOTE | PERMALINK | REPORT

SilenXynh EDIT: Oh, you lucky dog. How I wish I'd just finish these exams and enjoy freedom - you at Uni now? benniu I'm really bad at probability. To tell you the truth, I didn't actually read past the first four words... but which year is the question from?

My Characters: realmdefendr - 65 Scania Hunter

SilentXynh + PM | QUOTE | PERMALINK | REPORT

First year uni at UNSW :P I have semester exams this Friday and Saturday LOL Work is punishment for ineffective procrastination EDIT: done my attempt, feel free to correct me.

My Characters: Aussenritter - 90 Scania Dawn Warrior

ElementSteal 10/25/10 + PM | QUOTE | PERMALINK | REPORT

Q1) Does w=1? P(same colour) = ( 3/ w+3 x 2/ w+2 ) + ( w / w+3 x w-1/ w+2 ) 1/2 = ( 6/ w^2 + 5w + 6 ) + ( w^2 - w / w^2 + 5w + 6 ) w^2 - w + 6 / w^2 + 5w + 6 = 1/2 w^2 - w + 6 = 1/2w^2 + 5/2w + 3 w^2 - 7w + 6 = 0 (w-6)(w-1) = 0 w = 1 , 6 However using the different procedure, when w = 6, P (same colour) is not = to 5/8 w = 1 is the only solution I think

My Characters: ElementSteal - 82 Bootes Chief Bandit

SilentXynh 10/25/10 + PM | QUOTE | PERMALINK | REPORT

[quote] ElementSteal : Q1) Does w=1? P(same colour) = ( 3/ w+3 x 2/ w+2 ) + ( w / w+3 x w-1/ w+2 ) 1/2 = ( 6/ w^2 + 5w + 6 ) + ( w^2 - w / w^2 + 5w + 6 ) w^2 - w + 6 / w^2 + 5w + 6 = 1/2 w^2 - w + 6 = 1/2w^2 + 5/2w + 3 w^2 - 7w + 6 = 0 (w-6)(w-1) = 0 w = 1 , 6 However using the different procedure, when w = 6, P (same colour) is not = to 5/8 w = 1 is the only solution I think [/quote] You got the same answer as me, so either we're both right or we're both wrong :P I'm leaning toward the former :D

My Characters: Aussenritter - 90 Scania Dawn Warrior

PewPewPhoton 10/25/10 + PM | QUOTE | PERMALINK | REPORT

Q2)A rhombus has half the area of a square with the same side-length the ratio of the long to short diagonal is (A) 2+ root3 (B) 2-root3 (C) 1/2 (D) 2 (E) root3 ? I'm not too sure what this question is asking =S Are A,B,C,D and E the ratios of the diagonals? o.O And yay~~~~~~ Fellow aussies =3

benniu 10/25/10 + PM | QUOTE | PERMALINK | REPORT

realmdefendr I don't know =D but its from Dr Du homework (if you know who that is)

My Characters: ShiftySteve - 35 Bera Blade Acolyte

PewPewPhoton + PM | QUOTE | PERMALINK | REPORT

Nope~ Just success one o.o" Um I'm really not familiar with that type of format o.o" It first looked like multiple choice and I was like "MC is back in maths... in the HSC?~ Hoo rah!" Does it have a diagram with those corresponding letters? Or how about the answers? I'm usually good with explaining an ambigious step.

SilentXynh + PM | QUOTE | PERMALINK | REPORT

The question for Q2 sounds very Engrish-y, I myself am trying to work out what it's asking =( To me, it looks like you'll have to do something like: Letting x and y be the diagonals of a rhombus and z be the sides, (x/2)^2 + (y/2)^2 = z^2, then find a property of the square and find the ratio of x to y :S

My Characters: Aussenritter - 90 Scania Dawn Warrior

PewPewPhoton 10/25/10 + PM | QUOTE | PERMALINK | REPORT

Lololol speaking about Engrish, 2012 HSC is going to be full of it =3 Lucky I'm finished this year~ ^^" By the way 2u was hell... T.T Oh well, time to redeem myself in 3u and physics =D I'm thinking Q2 has another part to it o.o I really can't see the question in it.

XxSluhsiexX 10/25/10 + PM | QUOTE | PERMALINK | REPORT

[quote] benniu : realmdefendr I don't know =D but its from Dr Du homework (if you know who that is) [/quote] Urgh, no way. I go to Dr Du as well, but I'm only in year 10 so I'm not even going to attempt to work out these questions. Focusing on my English essay right now

My Characters: XxSluhsiexX - 140 Bera I/L Arch Mage