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# why do i need to know about frequency distribution?

By David Moody on the 11th of June, 2012

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Frequency distribution is a tool. Tt is used for organising data. We use it to group data into categories and show the number of observations in each category.

Here are some  test scores from a science class.

18, 36,28,47,42,28,32,42,28,16,18,28,34,42,47,16,34

It's hard to get a feel for this data in this format. Because it is unorganized. To construct a frequency distribution,  you  should first identify the lowest and highest values in the list. The low value is 16 and the high is 47. The set of categories that would work here is 0-10, 11-20,21-30, 31-40, 41-50.

Class                               Frequency

0-10                                   0

11-20                                 4

21-30                                 4

31-40                                 4

41-50                                 5

Therefore we need to know about frequency distribution.

By Abi Wilson on the 19th of January, 2013

## Solve probability problems involving independent events

When it comes to solving probability problems in GCSE Maths it's important to know the differences between independent and dependent events, becuase these effect the probability outcome.

If two events are independent, then the outcome of one event have no effect on the outcome of the second. For example, if I flip a coin twice, whether the first toss landed heads or tails has no impact on how the second toss landed. The probability of getting heads first time was ½, and the probability of getting heads the second time was still ½.

These types of question are best solved using a probability tree diagram.

In order to solve probability problems using a tree diagram, we need to know that we multiply along the branches (for AND) and add vertically ( for OR).

Example:

A bag contains 4 red balls, 6 black balls. A ball is taken out of the bag at random and then replaced. Then another ball is taken out and then replaced.

To find out the probability that a black ball, then a red ball, can be done by multiplying the probability of getting a black ball (3/5) by the probability of getting a red ball (2/5) so the probability of getting a black ball then red ball is 3/5 x 2/5 = 6/25

To find the probability of getting a ball with each colour i.e. what is the probability of getting first a black then a red ball, and the probability of getting a red then a black ball. From our diagram we can see the probability of both is 6/25. So we need to add these to get 12/25

Now, let's see if you can solve some probability problems with independent events, just click on 'Test Questions'

Or you can Ask a Question online, and get help from the community.

## Follow the links below to see how this topic has appeared in past exam papers

AQA Unit 1 March 2011 (F) - Page 4, Question 2

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