ok so here goes....

the digits 3, 6, 7 and 8 will be used without repetition to form different 3 digit numbers. of all such numbers how many are greater then 500?

A. 6

B. 12

C. 18

D. 24

E. 48

i just dont know how to do this problem without writing out all the possible combinations, but on a timed test this wouldn't work because, i would run out of time.

i guessed 12 well 6 was too small, 48 and 24 are too big so it had to be 12 or 18. so i reasoned 4 numbers in 3 digit combinations 4 times 3 = 12?

sat may 2011 section 4 problem 11