SAT Subject Test Mathematics Level 2

46 . A

You can find    the mean    by  adding  these   terms   and dividing    the sum by  four,   the number  of

terms   in  the set.

Now divide  this    sum by  4:

47 . D

You can start   by  counting    the number  of  ways    this    outcome can occur.  There   are

ways    that    exactly two of  four    letters will    arrive  in  two days    or  sooner  (the    first   and second

letters,    the first   and third,  the second  and fourth, etc.).

The probability of  a   letter  failing to  arrive  in  two days    or  sooner  is  

So  the probability of  the first   two letters arriving    in  two days    or  sooner, and the other   two

arriving    later   than    that    is:

The probability of  any other   pair    of  letters arriving    in  two days    or  sooner  and the other   two

arriving    later   than    that    is  the same.   The probability of  any of  those   outcomes    occurring   is  the

sum of  all of  them.   Since   they    are the same,   the probability of  exactly two arriving    in  two

days    or  sooner  is  

48 . B