All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.

(i)

Firstly, the number of different friends is a fixed constant.

Secondly, the probability of successfully contacting a friend is constant.

(ii)

The probability of contacting a friend will vary from friend to friend, as some friend might not be free or contactable during that evening.

(iii)

(iv)

Since

by continuity correction

### KS Comments:

Students should be careful to write all assumptions in the context of question. I cannot stress the importance of this. Conditions for Binomial Approximation have to be well stated and explained. Lastly, remember to do continuity correction.

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