What does 'mean weight differs from 20g' mean in statistics?

[Biochemgirl2002]

Homework Statement

A sample of 100 flounders of a certain species has sample mean weight 21.5 grams and standard
deviation 8.4. Scientists want to determine if the mean weight differs from 20 grams.
a) At α = 0.05, is there enough evidence to conclude that the weight is different from 20? Use the p-value method.

Relevant Equations

i have no clue

i don't know what to do, but i am not asking help for the whole thing i am just wondering what it means by mean weight differs from 20g? from 1.5g-41.5g? or does it mean when the weight is not 20g

 

[WWGD]

I think they want you to construct a confidence interval about the sample mean and see if it includes the value 20.

 

[Stephen Tashi]

i am just wondering what it means by mean weight differs from 20g? from 1.5g-41.5g? or does it mean when the weight is not 20g

The scientists are interested in whether the mean weight of the population is (or is not) 20g. Their question is not whether the mean weight of the population is in the interval [1.5g, 41.5g].