Hello Zafar. The question is asking to find a midpoint between two numbers and to mark it on a line. A good way to think about this is if we consider a football field which is divided into sections as indicated by the white grid. If one player were to stand at the 50 yard line, and another player on the 0 yard line, the 25 yard line would be the location of the midpoint. If the player on the 50 yard mark moved 25 yards toward the goal, he would then be only 25 yards away from the goal. Likewise, if the player on the zero yard line was to move 25 yards into the field, he would also be 25 yards away from the goal.
This would be represented mathematically as (0 + 50) / 2, which equals 25. 0 + 25 = 25 and 50  25 = 25. 25 yards is the distance both players have to travel in order to meet in the middle.
More illustrations:
(9 + 10) / 2 = 19/2 = 9.5, the midpoint between 9 and 10. To check ourselves the following two equations must yield the same answer.
 9  9.5  = .5 and  10  9.5  = .5
11/26/2013

Yvonne W.