Variance / standard deviation

logicandtruth

New member
Hi all - I wonder if you can help please.

Watching a video on youtube to help me understand about the mean, variance and standard deviation but last part of video left me confused.

The speaker said the following for the formula for standard deviation: Consider if the variance is 200 for the first example and 2 for the second, please could someone explain in detailed simple terms why he calculated it to be 10 square roots of 2 and not 14. 14

Attachments

• 45.9 KB Views: 0

Jameson

Staff member
Hi there... just watched the video. Can you explain how you get 14? That will help me show where you are off. logicandtruth

New member
Hi there... just watched the video. Can you explain how you get 14? That will help me show where you are off. Hi Jameson - thanks for your response.

From timestamp 10:35 speaker starts to explain how he will calculate standard deviation using variance. As the variance in the example is 200, applying the formula used in the video you would have to find the square root of 200 which is 14. Instead he mentions the square root of 200 is equal to 10 square root's of 2 and I am not sure how/why he did this?

Jameson

Staff member
Hi again,

Ok so $\sqrt{200}$ is not 14. Let's do it together.

$\sqrt{200} = \sqrt{100 \times 2} = \sqrt{100} \times \sqrt{2} = 10\sqrt{2}$.

Does that help? logicandtruth

New member
Hi there,

Yes it now all makes sense as I now understand I essentially just needed to simplify the square root of an integer.

Thanks for your response, but please don't take it as a criticism but just posting an answer without explanation often does not help the intended recipient. Case in point, as someone not from a maths background motivated to improve, I went and did research where I learned the speaker was simplifying radical expressions. After reading more about this subject I also understood the rules such a
Hi again,

Ok so $\sqrt{200}$ is not 14. Let's do it together.

$\sqrt{200} = \sqrt{100 \times 2} = \sqrt{100} \times \sqrt{2} = 10\sqrt{2}$.

Does that help? s If any factors are raised to the power of 2, they can be moved outside of the square root.

Hi there,

Yes it now all makes sense as I now understand I essentially just needed to simplify the square root of an integer.

Thanks for your response, but please don't take it as a criticism but just posting an answer without explanation often does not help the intended recipient. Case in point, as someone not from a maths background motivated to improve, I went and did research where I learned the speaker was simplifying radical expressions. After reading more about this subject I also understood the rules such as If any factors are raised to the power of 2, they can be moved outside of the square root.

Best,