What is the total number of residents in the building?

Solution

Let the number of people who read ‘The Hindu and TOI (Only)’ be x Let the number of people who read ‘The Hindu and Economic Times (Only)’ be y. Let the number of people who read ‘TOI and Economics Times (Only)’ be z. Given that: 40 + 20 +x +y = 100 =>x+y = 40 ---- (i) 70 + 20 +x+z = 150 =>x+z = 60 ----(ii) 100 + 20 +y+z = 200 =>y+z = 80 -----(iii) Adding eq. (i), (ii) and (iii), we get 2 (x+y+z) = 180 x+y+x = 90 ----(iv) Now, subtracting (iv) by (i), we get z= 50 Now, subtracting (iv) by (ii), we get y= 30 Now, by subtracting (iv) by (iii), we get X=10 Total number of residents in the building = 40 + 70 + 100 + 10 + 50 + 30 + 20 = 320.