Another weird maths question

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

That's correct for a)
for b) and c) think about the fractions which do not wear a brace/are not left handed

That's correct for a)
for b) and c) think about the fractions which do not wear a brace/are not left handed

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

a) 1/16
b/ 7/16
c 14/16 = 7/8

dld

Hey thanks for the answer but the probability dont add up to 1? so how would a be correct?

How did you work it out??

You just multiply the probabilities, for example, say that the chance of having a dog was 1/3 and the chance of having a dog is 1/5.

To calculate the chance of having a dog, but not a cat is

2/3 * 1/5 = 2/15

It is 2/3 because 1/3 of people have cats, 1 - 1/3 = 2/3

draw a probability tree
___________
I__________ I
LH ________RH
I___ _ I___ I ____I
B ___NB _B ___NB
(Note: B=brace and NB=no brace)

Simply follow the tree down the correct paths and multiply the corresponding probabilities
You can calculate the probabilities for RH and NB because in each line the probability will add to 1, so the probability of being left handed, plus the probability of being right handed = 1.


So for a, you want the path that has 'left handed' and 'brace'. Therefore you are correct in multiplying the probabilities for these 2

for question B, you want to follow the path of LH then NB, multiplying these probabilities.


Edit: Sorry the formatting is a little off so its not a great tree

But how will it work when the probabilities don't add up wot 1?

Well, you multiply them (as I have done)

The probabilities only add up to one if it's the same thing, if you get me (not the best at explaining things).

Say if you had your name in a hat, along with 9 other people from the class. The chance of you being picked is 1/10. However, the chance of someone being picked is from your class (i.e everyone but you) is 9/10. 1/10 + 9/10 is 10/10 = 1 (as someone is going to be picked from a hat).

If we said there was a 1/10 chance of you being picked from the hat AND being picked for, I don't know, to take the register back out of the 10 people, the chance of you doing both is 1/10 * 1/10 = 1/100. However, 1/10 + 1/10 =/= 1 as both instances are independent of each other (i.e. there isn't a 100% chance you will be picked for either).

dld

Hey thanks for the answer but the probability dont add up to 1? so how would a be correct?

Also you got a 9 in maths and 8 in english HOW :/

Please give me tips I am aspiring for those grades this year

They don't have to add up to one, as the probabilities are mutually exclusive.

I'm not sure tbh...maths just seems to come to me naturally and the English, while I put a lot of work in, was a total shock! Basically you need to listen to your teachers, they will give you the skills and feedback needed to get the high grades, then do plenty of practise questions (make sure you know your equations/quotes!) and apply all your knowledge effectively in the exam

ic

For English any specific way you wrote your answers (recipe?) + When did you start revising to get these amazing grades. I am revising moderatly now but alot of people are telling me it is too much?