Answer:
Standard deviation is needed
Explanation:
The average length of the crayfish from the stream A is given i.e the mean value 10 cm
also, the average length of crayfish from stream B is given i.e the mean value 6 cm
Now,
to find out if there is any significant difference between the average length of crayfish in stream A and the average length of crayfish in stream B we need the standard deviation of the measured lengths.
The standard deviation depicts the deviation of a value from the group.
Thus, it will help in knowing if there is any significant difference.
