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A class of 40 set out to determine the population of lizards in a bound field measuring 200 metres by 100 metres using the capture-recapture method.

In their first outing, the students captured a total of 360 lizards all of which were marked with indelible ink and then released back into the field.

After a one week interval the students went back into the field and caught a total of 250 lizards out of which 150 bore the indelible ink mark.

The population density of the lizards in the field is?