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In limited versions of BASIC, identifiers can be 1 or 2 characters long, but the first must be a letter and the second a letter or digit.

I thought that there are 26 possibilities for the first position and 36 for the second (26 + 10 for the digits), which would give 26*36 = 936 possible identifiers. The book however says the answer 962, so I'm not sure what I'm doing wrong.

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Or more precisely 2.5 from Frederick Solomon's Probability and Stochastic Processes. – the_enigma Oct 23 '12 at 23:29
Great! Thanks for that. I think it's worthwhile mentioning these references in case it saves the reader time. [I'll delete my original comment, since yours is the real source.] – Douglas S. Stones Oct 23 '12 at 23:33

You overlooked the $37$-th possibility for the second character: no second character at all, (i.e., a one-character identifier).

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Ah, that makes sense. Thanks. – the_enigma Oct 23 '12 at 23:20

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