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How many numbers with two or more digits can be formed with the digits 1,2,3,4,5,6,7,8,9, so that in every such number, each digit is used at most once and the digits appear in the ascending order?
Correct answer is '502'. Can you explain this answer?
Verified Answer
How many numbers with two or more digits can be formed with the digit...
It has been given that the digits in the number should appear in the ascending order. Therefore, there is only 1 possible arrangement of the digits once they are selected to form a number. There are 9 numbers (1,2,3,4,5,6,7,8,9) in total.
2-digit numbers can be formed in 9C2 ways.
3-digit numbers can be formed in 9C3 ways
..................................................
9-digit number can be formed in 9C9 ways.
We know that nC0 + nC1 + nC2 + …………. nCn= 2n
=> 9C0 + 9C1 + 9C2 + ....9C9 = 29
9C0 + 9C1 + ...9C9 = 512=> We have to subtract 9C0 and 9C1 from both the sides of the equations since we cannot form single digit numbers.
=> 9C2 + 9C3 + ... + 9C9 = 512 − 1 – 9
9C2 + 9C3 + ... + 9C9 = 502
=> Therefore, 502 is the right answer.
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Most Upvoted Answer
How many numbers with two or more digits can be formed with the digit...
There are several steps involved in solving this problem. Let's break it down step by step:

Step 1: Understanding the problem
The problem asks us to determine the number of numbers with two or more digits that can be formed using the digits 1, 2, 3, 4, 5, 6, 7, 8, and 9. The conditions for these numbers are that each digit is used at most once, and the digits appear in ascending order.

Step 2: Analyzing the conditions
To form such numbers, we need to consider the following conditions:
- Each digit can be used at most once: This means that no digit can be repeated in the number.
- The digits appear in ascending order: This means that the digits should be arranged in increasing order from left to right.

Step 3: Determining the possible arrangements
To find the number of arrangements that satisfy the given conditions, we can use combinatorics. Since the digits should appear in ascending order, we can choose any subset of the digits and arrange them in ascending order. The number of ways to do this can be calculated using combinations.

Step 4: Calculating the number of arrangements
To calculate the number of arrangements, we need to consider all possible subsets of the digits and arrange them in ascending order. Let's break it down further:

- Numbers with 2 digits: Since there are 9 digits to choose from, we can select any 2 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 2) = 9! / (2! * (9-2)!) = 36.

- Numbers with 3 digits: We can select any 3 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 3) = 9! / (3! * (9-3)!) = 84.

- Numbers with 4 digits: We can select any 4 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 4) = 9! / (4! * (9-4)!) = 126.

- Numbers with 5 digits: We can select any 5 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 5) = 9! / (5! * (9-5)!) = 126.

- Numbers with 6 digits: We can select any 6 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 6) = 9! / (6! * (9-6)!) = 84.

- Numbers with 7 digits: We can select any 7 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 7) = 9! / (7! * (9-7)!) = 36.

- Numbers with 8 digits: We can select any 8 digits and arrange them in ascending order. This can be calculated using combinations: C(9, 8) = 9! / (8! * (9-8)!) = 9.

- Numbers with 9 digits: We can select all 9 digits and arrange them in ascending order
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How many numbers with two or more digits can be formed with the digits 1,2,3,4,5,6,7,8,9, so that in every such number, each digit is used at most once and the digits appear in the ascending order?Correct answer is '502'. Can you explain this answer?
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