Let S=\ 2,3,4,5,6,7,9\ . How many different 3-digit numbers (with...

$\therefore n(s)=7$ For 3 digit numbers less than 500 (repetion not allowed) Numbers of digits choice for hundred place $(2,3,4)=3$ Numbers of digits choice for tens place $=6$ Numbers of digits choice for once place $=5\therefore$ Total number of 3 digit numbers less than 500 $=3 \times 6 \times 5=90$