The number of words, with or without meaning, that can be formed by taking 4 letters at a time from the letters of the word 'SYLLABUS' such that two letters are distinct and two letters are a like, is _________.
Ans : 240
SYLLABUS
S - 2, L - 2, A, B, Y, U
Required =
Four fair dice are thrown independently 27 times. Then the expected number of times, at least two dice show up a three or a five, is _______