This type of sample refers to convenience sampling or grab sampling or accidental sampling.
Convenience sampling is a non-probability type sampling that includes the population which is nearby or available in your zone.
This type of sampling is handy when you need to know about a particular data in less time .Although the result may be somewhat biased because of a certain type of population may exist close to you.This method is most useful for Pilot testing.
A convenience sample <em>is a sort of sampling technique where it is simple to contact or reach the sample from a group of individuals.
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The participants are chosen simply <em>because they are simplest to select for the research and the researcher did not consider choosing topics representing the whole population.</em>
In this question, it's asking you to find the number when 90 is subtracted by 35%. So, you find 35% of 90 which is 31.5 and you minus it from 90 = 58.5.