Question

there are 100 in a class and they attend a test.20 students are failed in both the subjects. 50students pass in subject a. 60 students passed in subject b. how many students passed in subject a only. a) 20 b) 30 c) 15 d) 25

Answer 1

20 student is passed in subject a only

Answer 2

Answer: Option 'a' is correct.

Step-by-step explanation:

Let the number of students be passed in subject a be n(a).

Let the number of students be passed in subject b be n(b).

Since we have given that

n(a) = 50

n(a') = 100 - 50 =50

n(b) = 60

n(b') = 100-60 = 40

n(a'∩b') = 20

So,n(a∩b)'=n(a'∪b')=n(a)'+n(b)'-n(a'∩b') = 50+40-20=70

n(a∩b)= n(U)- n(a∩b)'=100-70=30

so, we need to find the number of students passed in subject a only.

So, it becomes,

n(only a ) = n(a) - n(a∩b) = 50-30 = 20

Hence, option 'a' is correct.