Can you solve this maths question?

Oh · June 05, 2015, 09:37:50 AM

Quote

There are n sweets in a bag. Six of the sweets are orange. The rest of the sweets are yellow.

Hannah takes a sweet from the bag. She eats the sweet. Hannah then takes at random another sweet from the bag. She eats the sweet.

The probability that Hannah eats two orange sweets is 1/3. Show that n²-n-90=0

This was a question on a GCSE maths exam. For Americans, 16 year olds would be answering this.
The reason I ask is because I've seen a lot of GCSE students complain about it on social media.
I just did it in like 10 seconds, so yeah.

Answer:

Spoiler

NO CHEATING CUNT ACTUALLY TRY AND ANSWER IT

Spoiler

n²-n-90=0
Factorise it:
(n-10)(n+9)=0
so n=10 or n=-9, you can't have -9 sweets, so it's 10.

So basically ignore everything, and just factorise the equation.

Apparently, you have to actually form the equation, so:

probability of picking orange first = 6/n
probability of picking orange second = 5/(n-1)
So the probability of picking the orange twice = (6/n) * (5/n-1)
However, it said in the question that the probability of picking it twice is 1/3, so
(6/n) * (5/n-1) = 1/3
multiplying gives you:
(30/n(n-1)) = 1/3
rearrange to get:
(n^2 - n)/30 = 3
n^2 - n = 90
n^2 - n - 90 = 0
there is your equation, factorise, you get n = 10.

cxfhvxgkcf-56:7 · June 05, 2015, 09:52:24 AM

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Oh · June 05, 2015, 09:53:52 AM

Quote from: kill yourself on June 05, 2015, 09:52:24 AM

>summer

>giving a fuck about academia

Kek

it was to see if you smarter than a bunch of retard teenagers, obviously you're not, you may as well kill yourself.

The Lord Slide Rule · June 05, 2015, 09:57:51 AM

Um. . .the probability bit is irrelevant to the answer. Isn't it? Just solve the polynomial for n.

You get 10 and -9.

Oh · June 05, 2015, 10:00:52 AM

Quote from: SexyBarracuda on June 05, 2015, 09:57:51 AM

Um. . .the probability bit is irrelevant to the answer. Isn't it? Just solve the polynomial for n.

You get 10 and -9.

that's what I did first, but you've actually got to form the equation to show it exists.

The Lord Slide Rule · June 05, 2015, 10:04:29 AM

Quote from: Simseoooooooooooo on June 05, 2015, 10:00:52 AM

Quote from: SexyBarracuda on June 05, 2015, 09:57:51 AM
Um. . .the probability bit is irrelevant to the answer. Isn't it? Just solve the polynomial for n.

You get 10 and -9.
that's what I did first, but you've actually got to form the equation to show it exists.

I realize that now, I was unclear about what the question was asking too bad you waited until after I looked.

I do stupid shit like that all the time. I've got the reading comprehension skills of a chimpanzee.

Ren · June 05, 2015, 10:16:23 AM

Maths is the bane of my existence. I'm not even gonna try.

Girl of Mystery · June 05, 2015, 10:31:49 AM

How do I maths?

A Cheese Potato · June 05, 2015, 10:37:09 AM

the hypotenuse

Oh · June 05, 2015, 11:58:52 AM

Quote from: A Cheese Potato on June 05, 2015, 10:37:09 AM

the hypotenuse

A*

big dog · June 05, 2015, 12:15:35 PM

(6/n) * (5/(n-1)) = 1/3
90 = n(n-1)
n^2 - n - 90 = 0

Easiest shit ever why were people crying over this. It's basic probability.

Oh · June 05, 2015, 12:18:38 PM

Quote from: Fedorekd on June 05, 2015, 12:15:35 PM

(6/n) * (5/(n-1)) = 1/3
90 = n(n-1)
n^2 - n - 90 = 0

Easiest shit ever why were people crying over this. It's basic probability.

Congratulations on beings able to maths.

big dog · June 05, 2015, 12:19:16 PM

Quote from: Simseoooooooooooo on June 05, 2015, 12:18:38 PM

Quote from: Fedorekd on June 05, 2015, 12:15:35 PM
(6/n) * (5/(n-1)) = 1/3
90 = n(n-1)
n^2 - n - 90 = 0

Easiest shit ever why were people crying over this. It's basic probability.
Congratulations on beings able to maths.

I just put numbers in and hope for the best.

Solonoid · June 05, 2015, 12:56:39 PM

Lol, stupid Brit math.
That's the probability that the second candy is orange, not that both are.

Naru · June 05, 2015, 02:36:08 PM

Onion · June 05, 2015, 02:42:50 PM

I rearranged it as

n^2 = n+90

Which can only be 10.

Oh · June 05, 2015, 05:41:58 PM

Quote from: Orion on June 05, 2015, 02:42:50 PM

I rearranged it as

n^2 = n+90

Which can only be 10.

n = -9 works for that as well

Solonoid · June 05, 2015, 05:52:34 PM

Quote from: Simseoooooooooooo on June 05, 2015, 05:41:58 PM

Quote from: Orion on June 05, 2015, 02:42:50 PM
I rearranged it as

n^2 = n+90

Which can only be 10.
n = -9 works for that as well

Not if you're looking for positive numbers.