Find The Q1 (Quartile1) and Q3 (Quartile 3).

Age
1-10
11-20
21-30
31-40
41-50
51-60
61-70

f
7
9
10
9
5
6
8

cb
.5-10.5
10.5-20.5
20.5-30.5
30.5-40.5
40.5-60.5
60.5-70.5

cf
7
16
26
35
40
46
54


Please help me! Thank you .. :))

It is nice to know that you have started answering the question.
40.5 - 50.5 and 50.5 - 60.5 classes are not taken by you by oversight. Simply 40.5 to 60.5 is taken wrongly.

Thereafter find Q1 class = size of (N/4)th item = size of 54/4th item = size of 13.5 th item
Q1 class = 10.5 to 20.5
Formula of interpolation is to be used for finding exact Q1
Q1 = l + (N/4 - cf)/f * i
l = lower limit of the Q1 class = 10.5
N/4 = 13.5
cf is the cumulative frequency of the class preceding the Q1 class = 7
f is the simple frequency of Q1 class 9
i is the class interval of Q1 class = 10
Q1 = 10.5 + (13.5 - 7)/9 *10 = 10.5 + 7.22 = 17.72
Q3 class = size of (3N/4) th item = size of (3*54/4)th item = size of 40.5th item
Q3 class = 50.5-60.5
Q3 = 50.5 + (40.5-40)/6 *10 = 50.5 + 0.83 = 51.33