Question

An experiment consists of 400 observations and four mutually exclusive groups. if the probability of a randomly selected item being classified into any of the four groups is equal, then the expected number of items that will be classified into group 1 is _____. 25 100 125 150

Answer 1

There are four mutually exclusive groups, therefore, the probability of one item being classified into any of the four groups is 1/4 or 0.25. 

The expected number of items is calculated as the product of the probability and the total number of observations. For this problem, the probability of an item being classified to group 1 is 0.25 and the total number of observations is 400. Therefore, the expected number of items is 
     $Expected\:number\:of\:items=0.25\times 400=100$

The expected number is 100.