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Sagot :
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.
The total number of different three digit numbers that can be made using any of the digits 1,2,3,4,5,6,7,8,9 is 729 digits.
What is the rule of product in combinatorics?
If a work A can be done in p ways, and another work B can be done in q ways, then both A and B can be done in [tex]p \times q[/tex] distinct ways.
Remember that this count doesn't differentiate between order of doing A first or B first then doing other work after the first work.
Thus, doing A then B is considered same as doing B then A
We can use the rule of product as:
- we can use the analogy of filling each of the 3 places of the three digit number, and this filling doesn't require any ordering like fill the first place and then second etc.
- We can take those 3 place fillings as 3 different works to be done,e each one doable in 9 different ways.
For this case, the three digit number consider is going to have 3 places in it such that each place can have any of those 9 digits in them.
So each place can be filled in 9 ways.
There are 3 such places, so, using the rule of product, the filling of those places can be done in:
[tex]9 \times 9 \times 9 = 9^3 = 729 \: \rm ways[/tex]
Thus, the total number of different three digit numbers that can be made using any of the digits 1,2,3,4,5,6,7,8,9 is 729 digits.
Learn more about rule of product combinations here:
https://brainly.com/question/2763785
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