In a class of 40 students, 30 read chemistry and 20 read physics. If all the students read at least one if the subjects, find the probability that a student selected at rand from the class reads only chemistry

hi

40 students

30 read chemistry

20 read physics

so logical deduction is that 10 read chemistry and physics.  

So only 20 read only chemistry and only 10 read only physics.  

So read only chemistry is  20/40 = 1/2

Answer as a fraction =  1/2

Answer in decimal form = 0.5

Answer in percent form = 50%

All three represent the same idea, but in a different form.

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Work Shown:

30 read chem, 20 read physics

30+20 = 50 read either one, but this is over 40, so 50-40 = 10 students must read both

From that,

30-10 = 20 read chem only

20-10 = 10 read physics only

This makes the venn diagram you see below

Divide the number of people who read chemistry only (20) over the total number of people (40). This gives 20/40 = 2/4 = 1/2

Then you would use your calculator to find 1/2 = 0.5 = 50%

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