781 views

### There are 7 white socks and 4 black socks in a drawer. Two socks are taken out at random without replacement. Work out the probability that the two socks are the same colour

The probability of pulling out two socks of the same colour is n/m*(n-1)/(m-1) where n is the initial number of that type of sock and m is the total number of socks in the drawer. The reason that we take 1 away from n and m is because a sock has been taken away from the drawer, and this means the probability of picking that kind of sock again has changed.

Initially there are 7+4 = 11 socks in the drawer.

The probability of picking 2 white socks is 7/11 * 6/10 = 0.382

The probability of picking 2 black socks is 4/11*3/10 = 0.109

Therefore, to find the probability of picking two of the same colour of sock, we add the probability of picking two white socks and the probability of finding two black socks together.

0.382 + 0.109 = 0.491

11 months ago

Answered by James, a GCSE Maths tutor with MyTutor

## Still stuck? Get one-to-one help from a personally interviewed subject specialist

#### 780 SUBJECT SPECIALISTS

£18 /hr

Degree: Mathematics (Masters) - Bath University

Subjects offered:Maths, Further Mathematics

Maths
Further Mathematics

“Hi! I am studying Mathematics at Bath University and I am passionate about teaching, and learning mathematics.”

MyTutor guarantee

|  1 completed tutorial

£18 /hr

Degree: Environmental Geoscience (Bachelors) - Durham University

Subjects offered:Maths, Geology+ 2 more

Maths
Geology
Geography
Chemistry

“Third year Earth Sciences student at Durham; specialise in geochemistry and tutor in Earth sciences, Chemistry and Maths”

Trusted by schools

|  4 completed tutorials

£18 /hr

Degree: Philosophy, Politics and Economics (Bachelors) - Oxford, Worcester College University

Subjects offered:Maths, Spanish+ 5 more

Maths
Spanish
History
Economics
.TSA. Oxford.
-Personal Statements-
-Oxbridge Preparation-

“I am an aspiring teacher, with a clear and analytic approach to tutoring that comes from an extensive and varied educational background.”

Currently unavailable: for regular students

Degree: Physics (Masters) - Bristol University

Subjects offered:Maths, Physics

Maths
Physics

“I am a Physics student at the University of Bristol. I thoroughly enjoy studying physics and wish to spread some of my enthusiasm for science and maths to those who I teach. I have experience as a peer mentor at university, where I he...”

MyTutor guarantee

### You may also like...

#### Other GCSE Maths questions

A is the point (2, -6). B is the point (-3, 4). Find the length AB.

Expand and simplify (2x-5)(3x+4)

Adam is going to get a loan of £ 720 to help pay for the holiday. Adam will have to pay back the £ 720 plus interest of 15 %. He will pay this back in 12 equal monthly installments. How much money will Adam pay back each month?

What is the fraction of blue beads?

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this.