Question

In how many ways can one write the numbers 1, 2, 3, 4, 5, and 6 in a row so that given any number in the row, all of its divisors (not including itself) appear to its left

Answer 1

Answer:  25 ways.

Step-by-step explanation:

first we have  1,2,6. this can appear once.

4, can appear in twice.

1. 3 can appear in-between 2 and 6, this means 3 can appear 3times before 6.
2. 5 would appear 5 times.
3. after 6 3 can appear 2 more times.

$= (3+2) * 5\\= 5*5\\= 25ways$

by not including itself, an appearing on the left side. one number can be written 25ways