 This week on Planet Money, why do grocery stores sell peanut butter in like six different sizes of jars these days? We investigate the secret strategies behind package sizes. After this job, I will never walk through a grocery store in the same way ever again. You can't unsee it. And on How I Built This, entrepreneurs call in for business advice from host Guy Raz and the co-founder of Sunbum, Tom Rinks. That's on the next How I Built This and Planet Money from NPR.