Using examples, how can you look at a substance and determine if it is a pure substance or a mixture?

A pure substance is something that is not mixed with anything like like a jar of rice or a jar of marbles
A mixture is something that is mixed together like if you made lemonade and you mixed lemon juice and water and sugar together it's a mixture and another example is if you mix sand and rocks together it's a mixture I hope I helped you

The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .