Question

How many different three digit numbers can be made with 123456789

Answer 1

Answer:

84

Step-by-step explanation:

Since, the digit should be in ascending order, therefore we have to group 123456789 into 3–3 groups with its digits being in ascending order.

Step 1:

Select 1 as one digit

Step 2:

Select 2 as a 2nd digit.

Step 3:

We have 7 numbers (3,4,5,6,7,8,9) as a 3rd digit of a 3-digit number. Therefore, We have 7 numbers in the form of 12_.

Go back to Step 2 and Select 3 as a 2nd digit. Then, we have 6 numbers (4,5,6,7,8,9) as a 3rd digit of the form 13_.

Continue these steps till you get the number of 3-digit numbers in the form of 1__ to 189 which will be 28 numbers.

Go back to Step 1 now and select 2 as a 1st digit and in Step 2, start with 3 as a 2nd digit.

In step 3, you’ll have 6 numbers (4,5,6,7,8,9) as a 3rd digit of the form 23_.

Continue these steps till you find the number of the 3 digit number of the form 2__ to 289 which will be 21

Repeat the steps again to find the number of 3digit number of the form 3__ to 389 which will be 15.

Then find 4__ to 489, 5__ to 589, ……till 789

the answers will be like this

1__=28

2__=21

3__=15

4__=10

5__=6

6__=3

789 which is 1

Adding all these, you’ll get 84.