Final answer:
You can tell you've lathered your hands for 20 seconds by humming the "Happy Birthday" song twice. It's important to properly lather all parts of your hands to effectively remove pathogens.
Step-by-step explanation:
An easy way to ensure that you have lathered your hands for at least 20 seconds is to hum the "Happy Birthday" song from beginning to end twice. As you lather your hands, be sure to cover all areas, including the backs of your hands, between your fingers, and under your nails. It's essential to wash your hands often and use the proper handwashing technique as recommended by the CDC to remove pathogens that can lead to illness.