Question

In a library there are books that teach one or more of 4 subjects: History, Geography, Politics
and Economics. All the History books also teach Politics.
None of the books that teach Economics also teach History or Geography. All the books that
teach Politics also teach Geography. If the number of books that teach Economics is half of
those which teach Geography. If the total number of books in the library is 1500, how many
books teach Geography?​

Answer 1

Answer  1000

Explanation

All history books also teach politics!

Which means if we draw a venn diagram, history comes inside politics.

similarly, all politics also teach geography!

So politics comses inside Geography.

Now, none of the books that teach economics also teach history or geography.

So economics is not connected with any of the 3 subjects.

now given that

                     

                                 E=1/2 G

                                 2E - G =0                -------- 1

we find from the diagram that ,

 

                                E + G =1500          ----------2

1 + 2

                                 3E = 1500

                                  E = 500

Therefore,                 D=1000

Hope this helped you and if you are preparing for NATA like i am all the best!