# Mistake in the variance video at 5:50min

**URL:** <https://community.deeplearning.ai/t/mistake-in-the-variance-video-at-5-50min/357365>\
**Category:** Probability & Statistics for Machine Learning &...\
**Tags:** week-module-2\
**Created:** [June 16, 2023, 6:01am UTC](https://community.deeplearning.ai/t/mistake-in-the-variance-video-at-5-50min/357365 "2023-06-16T06:01:44Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Kevin\_Shey](https://avatars.discourse-cdn.com/v4/letter/k/ea666f/32.png) [@Kevin\_Shey](https://community.deeplearning.ai/u/Kevin_Shey)\
**Post date:** [June 16, 2023, 6:01am UTC](https://community.deeplearning.ai/t/mistake-in-the-variance-video-at-5-50min/357365/1 "2023-06-16T06:01:44Z")

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At 5:50 of the variance video, it was stated that E[X2] = 5, which is incorrect.

The example gave +$4 and +$6 for each of the outcomes. If it were 4 and 6, you will have

E[X2]= (4+6)/2 = 5

But that is incorrect because Game 2 is -$4 for Tails and +$6 for Heads. Then, E[X2] should be :E[X2] = (-4 +6)/2 = 1

This will lead to the conclusion that Game 2 is RISKER than Game 1 because the dispersion from the mean for Game 2 is magnitude 5 and the dispersion from Game 1 from the mean is magnitude 1.

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**Author:** ![lucas.coutinho](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/lucas.coutinho/32/155465_2.png) [@lucas.coutinho](https://community.deeplearning.ai/u/lucas.coutinho)\
**Post date:** [June 16, 2023, 1:59pm UTC](https://community.deeplearning.ai/t/mistake-in-the-variance-video-at-5-50min/357365/2 "2023-06-16T13:59:46Z")

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Hi @Kevin_Shey!

Actually the game should be Win 6 and Lose 4. It is a typo in the video that is already being fixed.

We are sorry for the inconvenience!

Thanks,  
Lucas

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<div class="post-metadata">

**Author:** ![Kevin\_Shey](https://avatars.discourse-cdn.com/v4/letter/k/ea666f/32.png) [@Kevin\_Shey](https://community.deeplearning.ai/u/Kevin_Shey)\
**Post date:** [June 16, 2023, 6:47pm UTC](https://community.deeplearning.ai/t/mistake-in-the-variance-video-at-5-50min/357365/3 "2023-06-16T18:47:20Z")

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Thank you for fixing it.

I do want to highlight that it is not just a typo problem. The lecture content actually uses the incorrect numbers (Win 6, Win 4) to draw the conclusion that both Game 1 & 2 are equally risky, which is incorrect and will be very confusing to the students.

Please highlight this to the class.