Given:
The doors on one side of hostel are numbered 1-20 .
On the other side they are numbered 21 to 40 .
1 is opposite 21.
To find:
The number is opposite 19.
Solution:
The doors on one side of hostel are numbered 1-20 .
On the other side they are numbered 21 to 40 . 1 is opposite 21. So, the pairs of opposite numbers are:
(1,21), (2,22), (3,23), (4,24), (5,25), (6,26), (7,27), (8,28), (9,29), (10,30),
(11,31), (12,32), (13,33), (14,34), (15,35), (16,36), (17,37), (18,38), (19,39), (20,40).
Therefore, the number opposite to 19 is 39.
