Question

Is their sufficient evidence to indicate a difference in mean serum uric acid levels between normal individuals and individuals with Downs's syndrome. the data consist of serum uric acid readings on 12 individuals with Down's syndrome and 15 normal individuals. The means are x̄1 is 4.5 mg/100 ml and x̄2 is 3.4 mg/100ml.

I am trying to find the standard deviation of the sample, how can I do this ? I dont have the population standard deviation.

Thanks