Math problem help??

We have a short response problem to do. and it asks for all the 3 digit numbers you can do with 2,4,7.
Without repeating to the number like 474, or 772, etc.
What are all the 3 digit numbers i can do with 2, 4 and 7?

247
274
742
724
472
427

You know that there are 6 of them, because 3!=6.

Just list them being systematic

247
274 (that's all w 2 as first digit)
427
472 (that's all w 4 as the first digit)

...

Can you figure the rest?

I hope this helps.

There are three numbers to chose from for the first then two an d finally. 3*2*1=6

247
274
427
472
724
742

247
274
427
472
742
724