Question

Compute how many 7-digit numbers can be made from the digits 1, 2, 3, 4, 5, 6, 7 if there is no repetition and the odd digits must appear in an unbroken sequence. (Examples: 3571264 or 2413576 or 2467531, etc., but not 7234615.)

Answer 1

Number of 7-digit numbers that can be made from the digit is 576

Explanation:

Given the data in the question;

digits ⇒ 1, 2, 3, 4, 5, 6, 7

Number of odd numbers in the given digits = 4

Number of even numbers in the given digits = 3

now, we take the odd digits as a single unit.

so, number of ways the odd digits can be arranged with the unit will be 4!.

Now, lets consider the unit of 4 odd digits with 3 even digits.

there are 4 units.

so the number of possible arrangements of these 4 units = 4!

hence, Number of 7-digit numbers that can be made from the digits will be;

⇒ Number of possible arrangements of 4 units × Number of ways in which the odd digits can be arranged within the unit.

⇒ 4! × 4!

⇒ 576

Therefore, Number of 7-digit numbers that can be made from the digit is 576