Question: A random survey of 400 students at a middle school in a city showed that 40 students were having glasses or contact lenses. Out of 200 students, how many would be expected to have glasses or contact lenses ?


A ) 10
B ) 4
C ) 20
D ) 40

Steps to derive

1 Number of students surveyed = 400.

2 Number of students having glasses or contact lenses out of 400 students = 40.

3 Probability of a student wearing glasses or contact lenses = 40 / 400.
 [Number of favourable eventsTotal number of possible outcomes.]

4 = 1 / 10
 [Simplify.]

5 Number of students who can be expected to have glasses out of 200 students = 200 × 1 / 10

6 = 20
 [Simplify.]



Hence the right answer is Option C

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