Question

How many numbers under 5,000 can be formed picking 4 digits from 1, 2, 3, 4, 7, 8, and 9, using each at most once?

Answer 1

no 5 and 6?

Answer 2

no just 1, 2, 3, 4, 7, 8, and 9. no 5 or 6

Answer 3

how i solve these problems
start by looking at the thousand place, what numbers can be put there for numbers less than 5000?

Answer 4

1, 2, 3, and 4

Answer 5

ok thats only 4 numbers, remember that

now the numbers can be used at most once

so if we look at the hundreds place, how many different numbers can be put there if one number is already used by hte thousand place?

Answer 6

6 can be used

Answer 7

good, now how about the tens place? remember a number is being used up in the thousand and hundreds

Answer 8

5.
Something like this?
4 6 5 4
4 6 5 4
4 6 5 4
4 6 5 4

Answer 9

multiply them up and what do you get?

Answer 10

1920

Answer 11

4*6*5*4

Answer 12

and thats how many numbers can be made with the following rules

Answer 13

What if the question asked for something like a 10 digit code from 20 different digits? I could I solve it without drawing it out?

Answer 14

20*19*18...*11?

Answer 15

20!/10!?

Answer 16

or 20*10, it depends on whether each number can be used only once

Answer 17

sorry, I meant if it had to be under 5 thousand and the numbers were all in order

Answer 18

This is saying that 1920 isn't right

Answer 19

in order, then you could probably just draw it out,

Answer 20

you have to calculate each of them seperately

Answer 21

123_ *4
124_ *3
127_ *2
128_ *1
134_ *3
137_ *2
138_ *1
147_ *2
148_ *1

Answer 22

etc etc etc

Answer 23

I don't understand?

Answer 24

*_ means the number of options that can be placed into the ones place

Answer 25

Still not sure I get it. How many that start with 1?

Answer 26

no idea, i didnt finish 1

Answer 27

I got it! 480!

Answer 28

Thanks!