Three different toys are stored in a warehouse. There are 15 000 toys in total and the number of each is shown in the table.
|Kinds of Stones||Bears||Dolls||Cars|
|Number of Stones||2 000||6 000||7 000|
A stratified sample of all the toys is taken and 420 cars are selected. Calculate the total number of toys in the sample.
Which type of random sample should be used to determine the subject preferences of a group of 400 students given the ratio of males to females is ?
In what sort of sampling does the researcher divide the population into separate groups called strata, then draw a probability sample from each group?