Originally Posted by

**shawli** first part:

A box contains 7 black cubes and 3 red cubes. Debra selects three cubes from the box without replacement. Let random variable *N* denote the number of red cubes selected by Debra.

second part:

Debra will win $2.00 for every red cube selected and lose $1.00 for every black cube selected. Let the random variable *W* denote Debra's winnings.

If *W=aN+b*, find *a* and *b*. Hence, find *E(W)*

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I'm okay with the first part ...but I'm not sure how to approach the second part.

Help please!