To find the relative frequency of the first class we first need to find its frequency, to help us do this we order the data which is shown below:
1047, 1052, 1081, 1161, 1172, 1214, 1222, 1231, 1268, 1307, 1313, 1329, 1330, 1332, 1343, 1402, 1402, 1412, 1421, 1447, 1455
The fifth class is made of the values from 1320 to 1389, we notice that the frequency of this class is 4. Now, the relative frequency is given by:
[tex]\frac{\text{ frequency of class}}{\text{ total frequency}}[/tex]
Then we have:
[tex]\frac{4}{21}[/tex]
Therefore, the relative frequency of the fifth class is 4/21
