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CBSE 10th Maths - Pair Of Linear Equations in Two Variables - Exercise 3.1

Question 1 Aftab tells his daughter, “Seven years ago, I was seven times as old as you were then. Also, three years from now, I shall be three times as old as you will be.” (Isn’t this interesting?) Represent this situation algebraically and graphically.
Solution:

Let Aftab's age be x years

Let, daughter's age be y years

Seven years ago,

Aftab's age = x - 7 years

Daughter's age = y - 7 years

According to question,

be

x-7=7(y-7)

x-7=7y-49

⇒x-7y=-42.........(i)

After 3 years,

Aftab's age = x + 3 years

Daughter's age = y + 3 years

According to question,

x+3=3(y+3)

x+3=3y+9

⇒x-3y = 6...........(ii)

The algebraic equation is represented by

x−7y = −42

x−3y = 6

For, x−7y = −42 or x = −42+7y

The Soluton table is

X -7 0 7
Y 5 6 7

For, x−3y = 6 or x = 6+3y

The solution table is

X 6 3 0
Y 0 -1 -2

The graphical representation is:

Question 2 The coach of a cricket team buys 3 bats and 6 balls for Rs.3900. Later, she buys another bat and 3 more balls of the same kind for Rs.1300. Represent this situation algebraically and geometrically.
Solution:

Let us assume that the cost of a bat be ‘Rs x’

And,the cost of a ball be ‘Rs y’

to the question, the algebraic representation is

3x+6y = 3900

And x+3y = 1300

For, 3x+6y = 3900

Or x = $\dfrac{3900-6y}{3}$

The solution table is

X -300 100 -100
Y 500 600 700

For, x+3y = 1300

Or x = 1300-3y

The solution table is

X 1000 700 400
Y 100 200 300

The graphical representation is as follows.

Question 3 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.
Solution:

Let the cost of 1 kg of apples be ‘Rs. x’

And, cost of 1 kg of grapes be ‘Rs. y’

According to the question, the algebraic representation is

2x+y = 160

And 4x+2y = 300

For, 2x+y = 160 or y = 160−2x, the solution table is;

X 50 60 70
Y 60 40 20

For 4x+2y = 300 or y = (300-4x)/2, the solution table is;

X 70 80 75
Y 10 -10 0

The graphical representation is as follows;

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