EvaJager
stne
How many three digit numbers greater than 330? can be formed from the digits 1,2,3,4,5 and 6, if each digit can only be used once?
1)72
2)48
3)120
4)96
5)76
Find the number of 3 digit numbers greater than 300, and then subtract from them the number of three digit numbers between 300 and 330 formed with the given 6 digits.
ABC three digit numbers greater than 300 - total of 4*5*4=80, because a must be greater than 2, so 4 possibilities left; B 5 remaining, and C 4 remaining possibilities to choose from.
Between 300 and 330 there are 1*2*4=8 numbers with the given property: A = 3, 1 possibility; B can be only 1 or 2 (ABC < 330), so two possibilities; C the remaining 4 possibilities after choosing A and B.
Total possible choice 80 - 8 =72.
Answer: A.
Thank You Eva..
Thanks for opening up my mind
after seeing your solution I got my mistake
Here is another way to approach this question
so lets take two cases
first case: hundredth digit is 3 ,
hundred digit is 3 ,so one option only .
then tenth digit cannot be 1 and 2 ( as we cannot have 316 or 326 ,these are less than 330 )and also 3, as 3 has been used in hundredth position, so 3 options only, 4 ,5, 6.
and units digit can have 4 remaining options so 1*3*4 = 12 all digits greater then 330 but less than 400
second case : hundred digit is greater than 3 only 3 options 4,5,and 6
3*5*4= 60
we have 5 options for the second place because now the hundredth digit is more than 3 , so tenth digit can be any of the 5 remaining options.
(eg 413, 426, 436, etc )
so total 60 +12 = 72
Thank you Bunuel for the further links ....