9720, 3240, 1080, 360, 180, 40
Find the wrong number in the given series.

The correct option is 180.

To find the wrong number in the given series, let us analyze the pattern of progression from left to right by observing the mathematical operation connecting consecutive terms:

$9720÷3=3240$

$3240÷3=1080$

$1080÷3=360$

Following this pattern, each subsequent number in the series should be obtained by dividing the previous number by 3.

Applying the division rule to 360:

$360÷3=120$

Therefore, the next number should be 120 instead of 180.

Verifying with the last term using 120:

$120÷3=40$

This matches the final number in the series. Thus, 180 is the wrong number in the given series.