Raw data is the data that has not been organised well enough for use.
Example:
Given below are the marks (out of 25) obtained by 10 students of class (V A) in mathematics in a test.
18, 16, 12, 10, 5, 5, 4, 19, 20, 10

A bar graph is a graph that presents data with rectangular bars having heights or lengths showing the values that they represent.

Arranging the data in ascending order, we get, $0,0,1,2,3,4,4,5,6,8$.
On observing, there are 5 days$(0,0,1,2,3)$ that had a temperature of less than 4° C.

The number of times a particular value of data occurs is known as frequency. 
Here, in the given data set:
K, J, F, J, A, J, N, S, A, J, A, W, P, J, A, H, A, P, O, W, J, K, Z.

we observe that K is occurring twice, therefore the frequency of K is 2.

In a bar graph, we follow these rules
1)The width of the bars should be uniform throughout.
2)The gap between one bar and another should be equal throughout.

The number of times a particular value of data occurs is known as frequency. 

Given:
×, ×, ÷, -, ×, +, +, ÷, ×, +, -, +, +, -, ÷, ×

We observe that the '+' symbol is occurring 5 times and therefore the frequency of + is 5.

4, 6, 5, 5, 4, 6, 3, 3, 5, 5, 3, 5, 4, 4, 6, 7, 3, 5, 5, 7

Here, we see the number of families with 3 members is 4 and with 4 members is also 4.
So, the number of families with less than 5 members is 8.

Given:
$1$ drop = $2$ inches 
Wednesday = $8$ drops of rain

Therefore, inches of rain on Wednesday =$2\times 8=16inches$

Given:
$1$ drop = $4$ inches of rain

Number of drops on Saturday = $4drops$
Number of drops on Sunday = $9drops$
Therefore inches of rain on Saturday and Sunday
$=(4+9)\times 4$
$=13\times 4=52inches$