# Ncert Solutions For Class 9 Maths Ex 3.1

## Ncert Solutions For Class 9 Maths Chapter 3 Ex 3.1

Q1. How will you describe the position of a mobile phone kept on the study table to another person?
Solution:

For describing the position of a mobile phone kept on the study table, we take two lines, a perpendicular and a horizontal line. Considering the table as a plane(x and y axis) and taking perpendicular line as Y axis and horizontal as X axis respectively. Take one corner of table as origin where both X and Y axes intersect each other. Now, the length of table is Y axis and breadth is X axis. From The origin, join the line to the mobile phone and mark a point. The distances of the point from both X and Y axes should be calculated and then should be written in terms of coordinates.
Let the distance of the point from X- axis and Y- axis is x and y respectively, so the mobile phone will be in (x, y) coordinate.

Q2. Street Plan: There are 2 main roads in a city .They intersect each other, at the center of the city. East-West and North-South are the directions of the two roads. Rest  streets of the city are at 200 m from each other and are parallel to these roads. There are (five) streets in every direction. Using 1cm = 200 m as scaling unit, draw a model of the city. Representation of roads/streets will be given by single lines.A model which has cross streets in which one particular cross street is made by 2 streets in which one running from North to South direction and the other runs from the East to the West direction. Each of these cross streets are referred as in the following manner: Through which the second street runs from the north to the south and the fifth runs from the East to the West which meets at some crossing, then the cross street that intersect each other will be (2,5). Using this convention, Find:

(i) How many cross – streets can be referred to as (4,3)$(4,3)$.
(ii) How many cross – streets can be referred to as (3,4)$(3,4)$.

Solution:

(i) Only one street can be referred to as (4,3)$(4,3)$ (as clear from the figure).

(ii) Only one street can be referred to as (3,4)$(3,4)$ (as we see from the figure).