You are Here: Home >< Maths

# Complicated question or not? watch

1. In a class of students 1/3 are left handed and 1/8 wear a dental brace.
A student is selected at random.

What is the probability of that student.
a) is left handed AND wears a brace
b) is left handed but does not wear a brace
c) does not wear a brace AND is not left handed

Note: 1/3 and 1/8 DOES NOT = 1 :/

Any ideas? for a) I did : 1/3 * 1/8 but then this does not compute the probs DONT = 1
2. (Original post by Reversed Flash)
In a class of students 1/3 are left handed and 1/8 wear a dental brace.
A student is selected at random.

What is the probability of that student.
a) is left handed AND wears a brace
b) is left handed but does not wear a brace
c) does not wear a brace AND is not left handed

Note: 1/3 and 1/8 DOES NOT = 1 :/

Any ideas? for a) I did : 1/3 * 1/8 but then this does not compute the probs DONT = 1
a should be 1/3 * 1/8 giving 1/24..
b should be 1/3 * 7/8.. so on so on, should be right tbh.
3. (Original post by Relentas)
a should be 1/3 * 1/8 giving 1/24..
b should be 1/3 * 7/8.. so on so on, should be right tbh.
but the probabilities dont add up to 1?
4. (Original post by Reversed Flash)
but the probabilities dont add up to 1?
I dont understand what you mean.. 1/24 doesnt equal one? or are you talking about the sum of all answers?
5. (Original post by Relentas)
I dont understand what you mean.. 1/24 doesnt equal one? or are you talking about the sum of all answers?
1/3 + 1/8 = not equal to one. Surely they should?
6. (Original post by Reversed Flash)
1/3 + 1/8 = not equal to one. Surely they should?
nah, they dont. (idk if you do the "smile and kiss" method for adding fractions) but here's an example.
1/3 + 1/8 = (8+3)/(8*3)
that means 11/24 is what you get when you add them together. so yea, it doesn't equal one.
7. (Original post by Reversed Flash)
In a class of students 1/3 are left handed and 1/8 wear a dental brace.
A student is selected at random.

What is the probability of that student.
a) is left handed AND wears a brace
b) is left handed but does not wear a brace
c) does not wear a brace AND is not left handed

Note: 1/3 and 1/8 DOES NOT = 1 :/

Any ideas? for a) I did : 1/3 * 1/8 but then this does not compute the probs DONT = 1
Most of the students are neither left handed nor do they wear a dental brace.

1/3 of students are left handed
2/3 are not

1/8 of students wear a dental brace
7/8 of students do not

Some left handed people wear a dental brace but some do not.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: October 13, 2017
Today on TSR

### Exam Jam 2018

Join thousands of students this half term

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams