pandasandpens
Badges: 12
Rep:
?
#1
Report Thread starter 4 years ago
#1
Hi, basically ive been working through this questions and im not getting the right answer. Does anyone mind showing their workingg?? Thanks!!

Q) In a childs game there should be 7 triangles 3 of which are blue and 4 of which are red, and 11 Squares, 5 of which are blue and 6 of which are red. However, two pieces are lost.

Assuming the pieces are lost at random, find the probability that they are
(i) the same shape
(ii) the same colour
(iii) the same shape and the same colour
(iv) the same shape given that they are the same colour.
0
reply
Zacken
Badges: 22
Rep:
?
#2
Report 4 years ago
#2
(Original post by pandasandpens)
Hi, basically ive been working through this questions and im not getting the right answer. Does anyone mind showing their workingg?? Thanks!!

Q) In a childs game there should be 7 triangles 3 of which are blue and 4 of which are red, and 11 Squares, 5 of which are blue and 6 of which are red. However, two pieces are lost.

Assuming the pieces are lost at random, find the probability that they are
(i) the same shape
P(triangle) = 7/(7+11)
P(square) = 11/(7+11)

(i) = P(triangle 1) * P(triangle 2) + P(square 1)*P(square 2).
0
reply
Tetragon213
Badges: 11
Rep:
?
#3
Report 4 years ago
#3
i) Add up the number of shapes, and you get 19. First, find the probability that 2 are Triangles and add that to the probability that the 2 are Squares. You get:
7 x 6 + 11 x 10 which gives you 4
19 18 19 18 9
ii) Same process, but instead of using 7, 6 and 11, 10 you use 10, 9 and 8, 7
my calculator gives me a horrible number; 73 divided by 171

Basically, you work out the probability of getting what you want first time round, then work out getting what you want second time round and multiply, remembering to subtract 1 from the numerator and denominator for the second one since an item has already been taken out.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Current uni students - are you thinking of dropping out of university?

Yes, I'm seriously considering dropping out (29)
18.35%
I'm not sure (3)
1.9%
No, I'm going to stick it out for now (53)
33.54%
I have already dropped out (3)
1.9%
I'm not a current university student (70)
44.3%

Watched Threads

View All