Question

How many 4 digit numbers can be made using 1-7 without repating?

Answer 1

1111, 1117, 1177, 1777, 7777, 7771, 7711, 7771.

Answer 2

Step-by-step explanation:

We have to make 4 digit number without repetition using 1,2,3,4,5,6,7.

For this we have to fill 4 spaces ( _ _ _ _) with required numbers.

Now for 1st space, how many possible ways you can fill this space?

In 7 ways, because we have 7 number remaining.

( 7 _ _ _)

Now for 2nd space, how many possible ways we can fill this space?

In 6 ways, because we already used one digit in previous space so only 6 digits are remaining now.

( 7 6 _ _)

Now for 3rd space, how many possible ways we can fil this space?

In 5 ways, because we already used two digis in previous spac8 so only 5 digits are remaining now.

( 7 6 5 _)

At last for 4th space, there are 4 possible ways to fill this space because we already used three digits in previous space.

( 7 6 5 4)

So we have to multiple this to get maximum number of ways to make a 4 digit number without repetition.

7*6*5*4 = 840

Hope its help...