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

Ex.3.3 Q.1
Solve the following pair of linear equations by the elimination method and the substitution method:
(1) x + y = 5 and 2x – 3y = 4
(2) 3x + 4y = 10 and 2x – 2y = 2
(3) 3x – 5y – 4 = 0 and 9x = 2y + 7
(4) +
y = -1 and x –
y = 3
x + y =5 and 2x –3y = 4
By elimination method
x + y =5 ... (1)
2x –3y = 4 ... (2)
Multiplying equation (1) by (2), we get
2x + 2y = 10 ... (3)
2x – 3y = 4 ... (2)
Subtracting equation (2) from equation (3), we get
5y = 6
y =
Putting the value in equation (1), we get
x = 5 – ( ) =
Hence, x = and y =
By substitution method
x + y = 5 ... (1)
Subtracting y from both sides, we get
x = 5 – y ... (4)
Putting the value of x in equation (2) we get
2(5 – y) – 3y = 4
–5y = – 6
y = =
Putting the value of y in equation (4) we get
x = 5 –
x =
Hence, x = and y =
again
(2) 3x + 4y = 10 and 2x – 2y = 2
By elimination method
3x + 4y = 10 .... (1)
2x – 2y = 2 ... (2)
Multiplying equation (2) by 2, we get
4x – 4y = 4 ... (3)
3x + 4y = 10 ... (1)
Adding equation (1) and (3), we get
x + 0 = 14
Dividing both side by 7, we get
x = = 2
Putting in equation (1), we get
3x + 4y = 10
3(2) + 4y = 10
6 + 4y = 10
4y = 10 – 6
4y = 4
y = = 1
Hence, answer is x = 2, y = 1
By substitution method
3x + 4y = 10 ... (1)
Subtract 3x both sides, we get
4y = 10 – 3x
Divide by 4 we get
y = (10 – 3x) ÷ 4
Putting this value in equation (2), we get
2x – 2y = 2 ... (1)
2x – 2(10 – 3x) ÷ 4) = 2
Multiply by 4 we get
8x – 2(10 – 3x) = 8
8x – 20 + 6x = 8
14x = 28
x = 28 ÷ 14 = 2
y = (10 – 3x) ÷ 4
y = 4 ÷ 4 = 1
Hence, answer is x = 2, y = 1 again.
(3) 3x – 5y – 4 = 0 and 9x = 2y + 7
By elimination method
3x – 5y – 4 = 0
3x – 5y = 4 ... (1)
9x = 2y + 7
9x – 2y = 7 ... (2)
Multiplying equation (1) by 3, we get
9 x – 15 y = 11 ... (3)
9x – 2y = 7 ... (2)
Subtracting equation (2) from equation (3), we get
–13y = 5
y = –
Putting value in equation (1), we get
3x – 5y = 4 ... (1)
3x – 5(– ) = 4
Multiplying by 13 we get
39x + 25 = 52
39x = 27
x = =
Hence our answer is x = and y = –
By substitution method
3x – 5y = 4 ... (1)
Adding 5y on both sides we get
3x = 4 + 5y
Dividing by 3 we get
x = (4 + 5y) ÷ 3 ... (4)
Putting this value in equation (2) we get
9x – 2y = 7 ... (2)
9 ((4 + 5y) ÷ 3) – 2y = 7
On solve we get
3(4 + 5y) – 2y = 7
12 + 15y – 2y = 7
13y = – 5
y = –
x = {4 + 5 × (-5 ÷ 13)} ÷ 3
x = (4 – ) ÷ 3
x = {(52 - 25) ÷ 13} ÷ 3
x = 27 ÷ (13 × 3)
x =
Hence, we get x = and y = -
again.
(4) +
= – 1 and x –
= 3
By elimination method
+
= – 1 ... (1)
x – = 3 ... (2)
Multiplying equation (1) by 2, we get
x + = – 2 ... (3)
x – = 3 ... (2)
Subtracting equation (2) from equation (3), we get
= – 5
Dividing by 5 and multiplying by 3, we get
y = –
y = – 3
Putting this value in equation (2), we get
x – = 3 ... (2)
x – (–3) = 3
x + 1 = 3
x = 2
Therefore x = 2 and y = – 3.
By substitution method
x – = 3 ... (2)
Adding on both sides, we get
x = 3 + ... (4)
Putting the value in equation (1) we get
+
= – 1 ... (1)
(3 + ) ÷ 2 +
= – 1
+
+
= – 1
Multiplying by 6,
9 + y + 4y = – 6
5y = – 15
y = – 3
Therefore x = 2 and y = – 3