CAT 2005 — QA Question 30
Answer the next 2 questions based on the information given below.
Ram and Shyam run a race between points A and B, 5 km apart. Ram starts at 9 a.m. from A at a speed of 5 km/hr, reaches B, and returns to A at the same speed. Shyam starts at 9:45 a.m. from A at a speed of 10 km/hr, reaches B and comes back to A at the same speed.
A rectangular floor is fully covered with square tiles of identical size. The tiles on the edges are white and the tiles in the interior are red. The number of white tiles is the same as the number of red tiles. A possible value of the number of tiles along one edge of the floor is
Answer & solution
- A
10
12
- C
14
- D
16
Let each square tile have side = 1 unit
Let the length of the rectangular floor be m units and the breadth be n units.
Number of red tiles = (m – 2)(n – 2)
Number of white tiles = mn − (m – 2)(n – 2)
Now, (m – 2)(n – 2) = mn − (m – 2)(n – 2)
⇒ 2(mn – 2m – 2n + 4) − mn = 0
⇒ mn – 4m – 4n + 8 = 0
⇒ n(m – 4) = 4m − 8
⇒ n = 4(m – 2)/(m – 4)
Now, consider the options.
Option (a): If m = 10, n = 32/6, which is not possible as n is an integer
Option (b): If m = 12, n = 40/8 = 5, which is possible
Option (c): If m = 14, n = 48/10, which is not possible as n is an integer
Option (d): If m = 16, n = 56/12, which is not possible as n is an integer
Hence, option (b).