Relative frequencies

Calculating relative frequencies

Question A

A bag contains 50 coloured marbles.
This table shows how many marbles of each colour are in the bag.

Colour	Red	Yellow	Orange	Green	Blue
Number	10	5	20	5	10

One marble is picked at random from the bag.
What is the probability of the marble being red or yellow?

Solution

The bag contains the population of 50 marbles.

In this case the relative frequency is the probability and not just an estimate.
The outcomes of the experiment are equally likely.
There are 10 red marbles and 5 yellow marbles.

The probability of the event 'obtaining a red or yellow marble'	\(=\dfrac{10+5}{50}\)
	\begin{align}&=\dfrac{15}{50}\\ &=\dfrac{3}{10} = 0.3. \end{align}

 

Calculating relative frequencies: QB