Joyce works in a toy factory maintaining machines. Machines should inject exactly 500 grams of plastic into a mold to make a toy plane. Joyce wonders if these toy machines might need cleaning, but it's a lot of work taking apart the machines to do a proper job. She grabs planes from 24 different machines at random and weighs them. Her average is 495 grams. She knows there's a standard devation of 10 grams for all machines (Joyce has been doing this for a while). What is Joyce's conclusion as a result of this test