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# S1 E(X) questions watch

1. Hi can someone explain why E(X) is 2 here? The answers at the back say its 2 because its symmetrical but I dont understand?

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2. (Original post by jessyjellytot14)
Hi can someone explain why E(X) is 2 here? The answers at the back say its 2 because its symmetrical but I dont understand?

Posted from TSR Mobile
Well, it's because symmetry. But another way to see it is:

But you know that probabilities sum to one, so: , back-subbing:

.
3. (Original post by Zacken)
Well, it's because symmetry. But another way to see it is:

But you know that probabilities sum to one, so: , back-subbing:

.
no full solutions!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!
4. (Original post by aymanzayedmannan)
no full solutions!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!
5. (Original post by jessyjellytot14)
Hi can someone explain why E(X) is 2 here? The answers at the back say its 2 because its symmetrical but I dont understand?

Posted from TSR Mobile
The x values either side of 2 are the same distance from 2 and have the same probability. That is the symmetry that they are talking about.

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Updated: February 25, 2016
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