i really need some math expert
i have a grade 12 data management test next week and got stuck on this question:
How many odd four-digit numbers, all of the digits different, can be formed from the digits 0 to 7, if there must be a 4 in the number?
the answer is 320
i know it's total odd number - total odd number without 4, but i keep getting 360.. help plzz
October 14, 2012
1 Comment • Newest first
List them all? o.o
Well, I'm not good at this or anything, but:
The last number must be odd, leaving 4 options for the last number, and since it can't be 4, that constraint is left alone.
The first number can be anything (7 options; I'm assuming we already chose the last number); the second can be anything but the first (6); and the third can be anything but the other 2 (5) but since one number HAS to be 4, there's another limit; if the other 2 numbers aren't 4, that one HAS to be 4 (1).
I probably totally butchered this problem