Question

How many four digit numbers are there

Answer 1

Answer:

using arithmetic progression

a=1000

d=1000-1001

 =1

an=9999

an=a+(n-1)d

9999=1000+(n-1)1

9999-1000=n-1

8999=n-1

n=8999+1

n=9000

therefore , there are 9000 4 digit terms

pls mark brainliest

Answer 2

Answer:

No. of digits = 4

Number of numbers that can be formed from 4 digits = 9 × 10 × 10 × 10 = 9000 numbers

Explanation:

Let's use P&C for the solution:

We have to fill 4 digits, and we have 10 numbers to do so, I.e, from 0 to 9.

But, we can fill the first place with any no. EXCEPT 0. Because, if a no. starts with 0, then it becomes a 3 digit or 2 digit or 1 digit no. (example: 0005 is 5 which is a one digit no. or 0038 is 38 which is a 2 digit no.)

So, we have 9 ways of filling the first place.

Let's come to the 2nd place. We can now use 0 also to fill the 2nd place. (As 1000 is also a 4 digit no, or 6046 is also a 4 digit no.)

So, we have 10 ways of filling the 2nd place (0 to 9, all numbers )

Similarly, we have 10 ways to fill the 3rd and 4th place too.

Thus, the total no. of ways of forming 4 digits becomes = 9 × 10 × 10 × 10 = 9000

I hope you understood :)