In a study of 500 children from a city, 238 were randomly selected to receive a new vaccine. The other 262 children were randomly selected to receive a placebo. The children and the physicians did not know to which group they had been assigned. After five years, 22 of the 238 children who received the vaccine had been infected with malaria; while 28 out of the 262 children who received the placebo had been infected with malaria. A) Is this an experiment or an observational study?

B) What are the variables? Which are categorical/quantitative?

C) Using the information above, fill in the two-way table to determine whether the vaccine is effective.

Please hellppp (Statistics Math) worth 100 points