Theory➡ Standard Deviation (SD) is an indication of how spread the values are as compared to the Mean
➡ SD is equal to the Root Mean Square(RMS) of the distance of the values from the Mean
If we look at the sets then at first glance following is the observation
(I) {55, 56, 57, 58, 59} -> Numbers are very close to the Mean (which is 57). So, SD will be Small.
(II) {41, 57, 57, 57, 73} -> Two numbers are very far from the mean of 57. Both 41 and 73 are at a distance of 16 from 57.(on either side)
(III) {57, 57, 57, 57, 57} -> All numbers are same so SD will be 0.
So, Sequence of SD will be
III < I < II
So,
Answer will be D.
If you want to learn how to calculate SD then the calculation is as follows(I) {55, 56, 57, 58, 59}Mean = 57 (middle value as the numbers are consecutive numbers)
Variance = \(\frac{(55-57)^2 + (56-57)^2 + (57-57)^2 + (58-57)^2 + (59-57)^2 }{ 5}\)
= \(\frac{(-2)^2 + (-1)^2 + 0^2 + 1^2 + 2^2 }{ 5}\)
= \(\frac{4 + 1 + 0 + 1 + 4 }{ 5}\) = \(\frac{10}{2}\) = 5
SD = \(\sqrt{Variance}\) = \(\sqrt{5}\)
(II) {41, 57, 57, 57, 73}Mean = 57 (middle value as the numbers are consecutive numbers)
Variance = \(\frac{(41-57)^2 + (57-57)^2 + (57-57)^2 + (57-57)^2 + (73-57)^2 }{ 5}\)
= \(\frac{(-16)^2 + 0^2 + 0^2 + 0^2 + 16^2 }{ 5}\)
= \(\frac{256 + 0 + 0 + 0 + 256 }{ 5}\) = \(\frac{512}{2}\) = 102.4
SD = \(\sqrt{Variance}\) = \(\sqrt{102.4}\) ~ 10
(II) {57, 57, 57, 57, 57}Mean = 57 (middle value as the numbers are consecutive numbers)
Variance = \(\frac{(57-57)^2 + (57-57)^2 + (57-57)^2 + (57-57)^2 + (57-57)^2 }{ 5}\)
= \(\frac{0^2 + 0^2 + 0^2 + 0^2 + 0^2 }{ 5}\)
= \(\frac{0 + 0 + 0 + 0 + 0 }{ 5}\) = 0
SD = \(\sqrt{Variance}\) = \(\sqrt{0}\) = 0
So, Sequence of SD will be
III < I < II
So,
Answer will be D.
Hope it helps!
Watch the following video to Learn the Basics of Statistics