NCERT Solutions
Class 11 Maths
Sequences and Series

Ex.15.3 Q.1
From the data given below state which group is more variable, A or B?
|
Marks |
10-20 |
20-30 |
30-40 |
40-50 |
50-60 |
60-70 |
70-80 |
|
Group A |
9 |
17 |
32 |
33 |
40 |
10 |
9 |
|
Group B |
10 |
20 |
30 |
25 |
43 |
15 |
7 |
Firstly, the standard deviation of group A is calculated as follows:
Here, h = 10, N = 150, A = 45
Mean x = A + [Σi=17 xi ÷ N] × h
= 45 + (-6 ÷ 150) × 10
= 45 - 0.4
= 44.6
Now, varience σ12 = (h2 ÷ N2) × [N × Σi=17 fi yi2 – (Σi=17 fi yi)2]
= (100 ÷ 22500) [150 × 342 – (-6)2]
= ( ) × 51264
= 227.84
So, standard deviation (σ) = √ (227.84) = 15.09
The standard deviation of group B is calculated as follows:
Mean x = A + [Σi=17 xi ÷ N] × h
= 45 + (-6 ÷ 150) × 10
= 45 - 0.4
= 44.6
Now, varience σ22 = (h2 ÷ N2) × [N × Σi=17 fi yi2 – (Σi=17 fi yi)2]
= (100 ÷22500) [150 × 366 – (-6)2]
= (1 ÷ 225) × 54864
= 243.84
So, standard deviation (σ) = √ (243.84) = 15.61
Since the mean of both the groups is same, the group with greater standard deviation will be more variable.
Thus, group B has more variability in the marks.