NCERT Solutions
Class 10 Maths
Pair of Linear Equations in Two Variables

Ex.3.2 Q.1
Solve the following pair of linear equations by the substitution method.
(1) x + y = 14; x – y = 4
(2) s – t = 3; +
= 6
(3) 3x – y = 3; 9x – 3y = 9
(4) 0.2x + 0.3y = 1.3; 0.4x + 0.5y = 2.3
(5) √2x + √3y = 0; √3x – √8y = 0
(6) x –
y = -2;
x +
y =
(1) x + y = 14 ... (1)
x – y = 4 ... (2)
From equation (1), we get
x = 14 – y ... (3)
Putting this value in equation (2), we get
(14 – y) – y = 4
14 – 2y = 4
10 = 2y
y = 5 ... (4)
Putting this in equation (3), we get
x = 9
So, x = 9 and y = 5
(2) s – t = 3 ... (1)
+
= 6 ... (2)
From equation (1), we get s = t + 3
Putting this value in equation (2), we get
t + +
= 6
2t + 6 + 3t = 36
5t = 30
t = ... (4)
Putting in equation (3), we get
s = 9
So, s = 9, t = 6
(3) 3x – y = 3 ... (1)
9x – 3y = 9 ... (2)
From equation (1), we get
y = 3x – 3 ... (3)
Putting this value in equation (2), we get
9x – 3(3x – 3) = 9
9x – 9x + 9 = 9
9 = 9
This is always true.
Hence, the given pair of equations has infinite possible solutions and the relation
between these variables can be given by y = 3x – 3
Therefore, one of its possible solutions is x = 1, y = 0.
(4) 0.2x + 0.3y = 1.3 ... (1)
0.4x + 0.5y = 2.3 ... (2)
0.2x + 0.3y = 1.3
Solving equation (1), we get
0.2x = 1.3 – 0.3y
Dividing by 0.2, we get
x = –
x = 6.5 – 1.5 y ... (3)
Putting the value in equation (2), we get
0.4x + 0.5y = 2.3
(6.5 – 1.5y) × 0.4x + 0.5y = 2.3
2.6 – 0.6y + 0.5y = 2.3
–0.1y = 2.3 – 2.6
y =
y = 3
Putting this value in equation (3) we get,
x = 6.5 – 1.5 y
x = 6.5 – 1.5(3)
x = 6.5 – 4.5
x = 2
So, x = 2 and y = 3
(5) √2x + √3y = 0 …………... (1)
√3x – √8y = 0 …………. (2)
From equation (1), we get
y = -√2x ÷ √3 …………. (3)
Put value of y in equation (2), we get
√3x - √2(-√2x ÷ √3) = 0
3x – 2x = 0
x = 0
Put value of x in equation (3), we get
y = 0
Hence, x = 0, y = 0
(6) x –
y = -2 ……… (1)
+
=
……………. (2)
From equation (1), we get
y =
x + 2
y = (3x + 4) ÷ 2
y = 3(3x + 4) ÷ (2 × 5)
y = (9x + 12) ÷ 10 ……… (3)
Put value of y in equation (2), we get
+ (
) × (9x + 12) ÷ 10 =
=> (20x + 27x + 36) ÷ 60 =
=> (47x + 36) ÷ 60 = 13 ÷ 6
=> (47x + 36) ÷ 10 = 13
=> 47x + 36 = 13 × 10
=> 47x + 36 = 130
=> 47x = 130 – 36
=> 47x = 94
=> x =
=> x = 2
Put value of x in equation (3), we get
y = (9 × 2 + 12) ÷ 10
=> y = (18 + 12) ÷ 10
=> y = 30 ÷ 10
=> y = 3
Hence, x = 2, y = 3