Mistakes that a lot of students make #Shorts

At Middle School, 3 out of 5 students make honor roll. What is the probability (in %) that a student does not make honor roll?

While tabulation of marks scored in an examination by the students of a class, by mistake the marks scored by one student got recorded as 93 in place of 63, and thereby the average marks increased by 0.5. What was the number of students in the class?

In a school,only 2 out of 5 students can participate in a quiz.What is the chance that a student picked at random makes it to the competition?

A teacher wants to estimate the creative abilities of her students then she should make:

In solving a problem that reduces to a quadratic equation,one student makes a mistake in the constant term and obtains 8 and 2 for roots.Another student makes a mistake only in the coefficient of first-degree term and finds -9 and -1 for roots.The correct equation is