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Ncert Solutions for Class 10

Pair of Linear Equations in Two Variables

Pair of Linear Equations in Two Variables

Exercise 3.1

1. Form the pair of linear equations in the following problems, and find their solutions graphically.

(i) 10 students of Class X took part in a Mathematics quiz. If the number of girls is 4 more than the number of boys, find the number of boys and girls who took part in the quiz.

(ii) 5 pencils and 7 pens together cost Rs 50, whereas 7 pencils and 5 pens together cost Rs 46. Find the cost of one pencil and that of one pen.

2. On comparing the ratios \(\frac{a_1}{a_2},\frac{b_1}{b_2}\) and \(\frac{c_1}{c_2}\), find out whether the lines representing the following pairs of linear equations intersect at a point, are parallel or coincident:

(i)   5x– 4y+ 8 = 0  and  7x+ 6y– 9 = 0

(ii) 9x+ 3y+ 12 = 0  and  18x+ 6y+ 24 = 0

(iii) 6x– 3y+ 10 = 0  and  2x– y+ 9 = 0

3. On comparing the ratios \(\frac{a_1}{a_2},\frac{b_1}{b_2}\) and \(\frac{c_1}{c_2}\), find out whether the following pair of linear equations are consistent, or inconsistent.

(i) 3x + 2y = 5;  2x – 3y = 7

(ii) 2x – 3y = 8;  4x – 6y = 9

(iii) \(\frac{3}{2}x+\frac{5}{3}y=7\);  9x – 10y = 14

(iv) 5x – 3y = 11;  –10x + 6y = –22

(v) \(\frac{4}{3}x+2y=8\);  2x + 3y = 12

4. Which of the following pairs of linear equations are consistent/inconsistent? If consistent, obtain the solution graphically:

(i) x + y= 5, 2x + 2y=10

(ii) x – y= 8, 3x – 3y= 16

(iii) 2x + y – 6 = 0, 4x – 2y – 4 = 0

(iv) 2x– 2y– 2 = 0, 4x– 4y– 5 = 0

5. Half the perimeter of a rectangular garden, whose length is 4 m more than its width, is 36 m. Find the dimensions of the garden.

6. Given the linear equation 2x+ 3y– 8 = 0, write another linear equation in two variables such that the geometrical representation of the pair so formed is:

(i) intersecting lines

(ii) parallel lines

(iii) coincident lines

7. Draw the graphs of the equations x– y+ 1 = 0 and 3x+ 2y– 12 = 0. Determine the coordinates of the vertices of the triangle formed by these lines and the x-axis, and shade the triangular region.

Pair of Linear Equations in Two Variables

Exercise 3.2

1. Solve the following pair of linear equations by the substitution method.

(i) x + y = 14   &   x – y = 4                        

(ii)  s – t = 3   &   \(\frac{s}{3}+\frac{t}{2}=6\)

(iii) 3x – y= 3   &   9x – 3y= 9

(iv) 0.2x + 0.3y = 1.3   &   0.4x + 0.5y = 2.3

(v)   \(\sqrt{2}x+\sqrt{3}y=0\)   &   \(\sqrt3x-\sqrt8y=0\)

(vi) \(\frac{3}{2}x-\frac{5}{3}y=-2\)   &  \(\frac{x}{3}x+\frac{y}{2}y=\frac{13}{6}\)    

2. Solve 2x + 3y = 11 and 2x – 4y = –24 and hence find the value of ‘m’ for which y = mx + 3.

3. Form the pair of linear equations for the following problems and find their solution by substitution method.

(i) The difference between two numbers is 26 and one number is three times the other. Find them.

(ii) The larger of two supplementary angles exceeds the smaller by 18 degrees. Find them.

(iii) The coach of a cricket team buys 7 bats and 6 balls for Rs 3800. Later, she buys 3 bats and 5 balls for Rs 1750. Find the cost of each bat and each ball.

(iv) The taxi charges in a city consist of a fixed charge together with the charge for the distance covered. For a distance of 10 km, the charge paid is Rs 105 and for a journey of 15 km, the charge paid is Rs 155. What are the fixed charges and the charge per km? How much does a person have to pay for travelling a distance of 25 km?

(v) A fraction becomes \(\frac{9}{11}\), if 2 is added to both the numerator and the denominator. If 3 is added to both the numerator and the denominator it becomes \(\frac{5}{6}\).  Find the fraction.

(vi) Five years hence, the age of Jacob will be three times that of his son. Five years ago, Jacob’s age was seven times that of his son. What are their present ages? 

Pair of Linear Equations in Two Variables

Exercise 3.3

1. Solve the following pair of linear equations by the elimination method and the substitution method:

(i) x+y=5 and 2x–3y=4

(ii) 3x+4y=10 and 2x–2y=2

(iii) 3x–5y–4=0 and 9x=2y+7

(iv) \(\frac{x}{2}+\frac{2y}{3}=-1\)  and   \(x-\frac{y}{3}=3\)

2. Form the pair of linear equations in the following problems, and find their solutions (if they exist) by the elimination method:

(i) If we add 1 to the numerator and subtract 1 from the denominator, a fraction reduces to 1. It becomes \(\frac{1}{2}\) if we only add 1 to the denominator. What is the fraction?

(ii) Five years ago, Nuri was thrice as old as Sonu. Ten years later, Nuri will be twice as old as Sonu. How old are Nuri and Sonu?

(iii) The sum of the digits of a two-digit number is 9. Also, nine times this number is twice the number obtained by reversing the order of the digits. Find the number.

(iv) Meena went to a bank to withdraw Rs 2000. She asked the cashier to give her Rs 50 and Rs 100 notes only. Meena got 25 notes in all. Find how many notes of Rs 50 and Rs 100 she received.

(v) A lending library has a fixed charge for the first three days and an additional charge for each day thereafter. Saritha paid Rs 27 for a book kept for seven days, while Susy paid Rs 21 for the book she kept for five days. Find the fixed charge and the charge for each extra day.