Choose the number that continues the series in the most sensible way.27 15 9 18 [?]

The pattern in the series seems to be division and multiplication alternately.

Starting with 27:

• 27 divided by 3 equals 9, which is not the next number in the series. So, this is not the pattern.
• 27 minus 12 equals 15, which is the next number in the series. So, this could be the pattern.

Continuing with 15:

• 15 divided by 3 equals 5, which is not the next number in the series. So, this is not the pattern.
• 15 minus 6 equals 9, which is the next number in the series. So, this could be the pattern.

Continuing with 9:

• 9 divided by 3 equals 3, which is not the next number in the series. So, this is not the pattern.
• 9 plus 9 equals 18, which is the next number in the series. So, this could be the pattern.

So, the pattern seems to be subtract 12, subtract 6, add 9. If we continue this pattern, the next operation would be subtract 12.

Therefore, the next number in the series would be 18 minus 12, which equals 6.