Alma brought her six-month-old son to the doctor for a well-baby visit. The doctor says that her son's weight is in the 20th percentile. What does this definitely mean?

He is in on the verge of 'lowest weighing 20% babies' & hence he is underweight.

Explanation:

Percentile in statistics is a comparative tool. It depicts the value below which a given percentage of observation in a group of observations fall.

Eg : A variable in 30th percentile means 30% of variable units are below it & remaining 70% are above it.

Doctor saying that Alma's son's weight is in 20th percentile means : only minor 20% babies weigh below him & major 80% weigh above him. So, it can be said that Alma's baby son is underweight relative to usual babies of his age.

answer; elasticity of the lungs decreases;

answer; ratification;