CBSE Notes, Lectures

CBSE - Mathematics - Pair of Linear Equations in Two Variables

Pair of Linear Equations in Two Variables

NCERT Exercise Exercise 3.1

The cost of 2 kg of apples and 1kg of grapes on a day was found to be Rs 160. After a month, the cost of 4 kg of apples and 2 kg of grapes is Rs 300. Represent the situation algebraically and geometrically

 

Let cost each kg of apples = Rs x
Cost of each kg of grapes = Rs y
Given that the cost of 2 kg of apples and 1kg of grapes on a day was found to be Rs 160
So that
= 160 … (i)
2x = 160 - y
x = (160 – y)/2
Let y = 0 , 80 and 160,  we get
x = (160 – ( 0 )/2 = 80
x = (160- 80 )/2 = 40
x = (160 – 2 × 80)/2 = 0
 

x 80 40 0
y 0 80 160


Given that the cost of 4 kg of apples and 2 kg of grapes is Rs 300
So we get
4x + 2= 300 … (ii)
Dividing by 2 we get
2x + y = 150
Subtracting 2x both side, we get
= 150 – 2x
Putting x = 0 , 50 , 100 we get
= 150 – 2 × 0 = 150
= 150 – 2 ×  50 = 50
= 150 – 2 × (100) = -50
 

x 0 50 100
y 150 50 -50


Algebraic representation,
2y = 160 … (i)
4x + 2y = 300 … (ii)

Graphical representation,

.