To solve the problem of finding the number of ways to write down the numbers from 0 to 9 in a sequence such that the even numbers are in increasing order and the odd numbers are in decreasing order, we can follow these steps:

Step 1: Identify Even and Odd Numbers

• Even numbers: 0, 2, 4, 6, 8
• Odd numbers: 1, 3, 5, 7, 9

Step 2: Understand the Constraints

• Even numbers must appear in the sequence in increasing order (0, 2, 4, 6, 8).
• Odd numbers must appear in the sequence in decreasing order (9, 7, 5, 3, 1).

Step 3: Determine Sequence Placement

The problem reduces to choosing positions for the even numbers in the sequence because, once these positions are chosen, the odd numbers will automatically occupy the remaining positions.

• The sequence has 10 positions.
• There are 5 even numbers, so we must choose 5 positions out of the 10 available for the even numbers. The remaining 5 positions will be occupied by the odd numbers.

Step 4: Calculate the Number of Combinations

The number of ways to choose 5 positions out of 10 is given by the binomial coefficient $\binom{10}{5}$.

$\binom{10}{5} = \frac{10!}{5!(10-5)!} = \frac{10 \times 9 \times 8 \times 7 \times 6}{5 \times 4 \times 3 \times 2 \times 1} = 252$

Step 5: Final Answer

Since there are 252 ways to choose 5 positions for the even numbers, there are 252 different sequences in which the numbers from 0 to 9 can be arranged such that the even numbers are in increasing order and the odd numbers are in decreasing order.

Conclusion

Thus, there are 252 ways to write down the numbers from 0 to 9 in a sequence where even numbers are in increasing order and odd numbers are in decreasing order.

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Would you like further details or have any questions? Here are some related problems you might find interesting:

1. How many ways can you arrange the numbers 0 to 9 such that even and odd numbers alternate?
2. What is the number of permutations of the numbers 0 to 9 without any restrictions?
3. How many ways can you arrange the numbers 0 to 9 such that no two even numbers are adjacent?
4. How many sequences can be made from the numbers 0 to 9 if only even numbers are allowed?
5. What if odd numbers are in increasing order and even numbers in decreasing order?
6. How many ways can you arrange 10 digits such that the sequence is palindromic?
7. What is the number of ways to arrange the digits 1 to 9 such that the sum of every two adjacent digits is even?
8. How many ways can you arrange the numbers 0 to 9