Question

MEDAL!!!

Permutations
How many numbers less than 600 can be formed using only digits between 3 and 7?

Answer 1

@jabez177 @robtobey

Answer 2

Well digits between 3 and 7 are: 4, 5, 6

We know that 6 cannot be the first number.

So it's either first slot is:

4 or 5.

Then next slot is either of the other two.

So 2*2*1 = 4 choices.

Answer 3

Then it won't be under 600.

Answer 4

I meant to say why can't 6 be the first number?

Answer 5

Oh yes.

Answer 6

So we can have 2 x 3! x 3!. Would that be correct?

Answer 7

I get that it equals to 72. But the answer key says that the answer is 105?

Answer 8

Hm.

Answer 9

@agent0smith

Answer 10

105 is 3*5*7, but that doesn't make sense.

I would say it's 3*5*5.