Q3 of 30 Page 62

Solve the following pair of linear equations by the substitution and cross-multiplication methods:

8x + 5y = 9


3x + 2y = 4

8x + 5y = 9........(i)

3x + 2y = 4........(ii)


From equation (ii), we get


....... (iii)


Substituting this value in equation (i), we obtain



32 - 16y + 15y = 27


-y = -5


Y = 5............. (iv)


Substituting this value in equation (ii), we obtain


3x + 10 = 4


x = -2


Hence, x = -2, y =5


Again, by cross-multiplication method, we obtain


8x + 5y - 9 =0


3x + 2y - 4 = 0





x = -2 and y = 5


More from this chapter

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2

For which values of a and b does the following pair of linear equations have an infinite number of solutions?

2x + 3y = 7


(a – b)x + (a + b)y = 3a + b - 2

2

For which value of k will the following pair of linear equations have no solution?

3x + y = 1

(2k – 1)x + (k – 1)y = 2k + 1

4

Form the pair of linear equations in the following problems and find their solutions (if they exist) by any algebraic method:

(i) A part of monthly hostel charges is fixed and the remaining depends on the number of days one has taken food in the mess. When a student A takes food for 20 days she has to pay Rs 1000 as hostel charges whereas a student B, who takes food for 26 days, pays Rs 1180 as hostel charges. Find the fixed charges and the cost of food per day.


(ii) A fraction becomes when 1 is subtracted from the numerator and it becomes when 8 is added to its denominator. Find the fraction.


(iii) Yash scored 40 marks in a test, getting 3 marks for each right answer and losing 1 mark for each wrong answer. Had 4 marks been awarded for each correct answer and 2 marks been deducted for each incorrect answer, then Yash would have scored 50 marks. How many questions were there in the test?


(iv) Places A and B are 100 km apart on a highway. One car starts from A and another from B at the same time. If the cars travel in the same direction at different speeds, they meet in 5 hours. If they travel towards each other, they meet in 1 hour. What are the speeds of the two cars?


(v) The area of a rectangle gets reduced by 9 square units, if its length is reduced by 5 units and breadth is increased by 3 units. If we increase the length by 3 units and the breadth by 2 units, the area increases by 67 square units. Find the dimensions of the rectangle.

1

Solve the following pairs of equations by reducing them to a pair of linear equations:



















(i)




(ii)




(iii)




(iv)




(v)




(vi)




(vii)




(viii)