Question

Of 80 students who scored first class marks in mathematics or English, 50 students got 1st class marks in mathematics and 10in English and mathematics. How many students got first class marks in English only

Answer 1

In order to solve this question, you need a little concept of Venn diagrams. It'll make the sum simpler.

In the image attached you can see the Venn diagram.

Acc.to question,
no.of students scored first class in maths only = 50.
no.of students scored first class in both maths and english = 10.
Let's assume no.of students scored first class in english only = x
Therefore,

50+10+x=80  (Since in total 80 students scored first class marks in mathematics or English)

or, 60+x=80
or,x=80-60
or,x=20(Ans).

Hence 20 students got first class marks in English only.