A fourdigit PIN number
aabb, where
a and
b are distinct digits, is a multiple of
15.Which values
of a are not possible?
(In reply to
Solution (spoil alert) by JayDeeKay)
So the possible values of a are when:
aa00 is divisible by 3, => 2a is mod3 => a=3, 6, 9
Then aabb = (3300, 6600, 9900)
aa55 is divisible by 3, => 2a+1 is mod 3 => a=1, 4, 7
Then aabb = (1155, 4455, 7755)
0 and 5 are values of b so they can't be values of a
Then the values of a that are not possible (to add 0 and 5) are only 2 and 8.

Posted by armando
on 20180206 14:55:40 