Harmonic mean between two positive numbers x and y, The simplified formula is 
I.e. you need to double the product of x and y then divide it by the sum of x and y...~
Answer:
No, Mr. Hernandez’s sample is random, not biased, large enough compared to the population, but 28 is not 20% of 90.
Step-by-step explanation:
At Lawson Middle School, Mr. Hernandez asked 90 randomly selected students from each grade level for their favorite subject.
90 randomly selected students from each grade level for their favorite subject, and 28 chose social studies as their favorite.
so, the percent of students who love social studies is given by:
28/90 x 100=31.11%
He used this data to draw the inference that out of the 250 middle school students, about 20% prefer social studies.
No, Mr. Hernandez’s sample is random, not biased, large enough compared to the population, but 28 is not 20% of 90.
