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Q1(ii):
Form the pair of linear equations in the following problems, and find their solutions graphically. (ii) 5 pencils and 7 pens together cost ` 50, whereas 7 pencils and 5 pens together cost ` 46. Find the cost of one pencil and that of one pen.

Solution :

Given:

1. The cost of 5 pencils and 7 pens together is ₹ 50.

2. The cost of 7 pencils and 5 pens together is ₹ 46.

To Find:

The cost of one pencil and the cost of one pen.

Step 1: Defining Variables

Let the cost of one pencil be $x$ and the cost of one pen be $y$.

Step 2: Formulating the Equations

Based on the given conditions, we can write the following system of linear equations:

Equation 1: $5x + 7y = 50$

Equation 2: $7x + 5y = 46$

Step 3: Finding Coordinates for Graphical Representation

To plot these lines, we find at least two points for each equation.

For Equation 1: $5x + 7y = 50 \implies y = \frac{50 - 5x}{7}$

$x$$y$
35
100

For Equation 2: $7x + 5y = 46 \implies y = \frac{46 - 7x}{5}$

$x$$y$
35
8-2

Step 4: Visual Representation

x y (3, 5)

Step 5: Solving the System

From the table of values, we observe that the point $(3, 5)$ satisfies both equations.

Verification for Equation 1: $5(3) + 7(5) = 15 + 35 = 50$ (Correct)

Verification for Equation 2: $7(3) + 5(5) = 21 + 25 = 46$ (Correct)

Step 6: Conclusion

Since the lines intersect at the point $(3, 5)$, the solution to the system is $x = 3$ and $y = 5$.

Final Answer: The cost of one pencil is ₹ 3 and the cost of one pen is ₹ 5.


More Questions from Class 10 Mathematics Pair of linear equations in two variable EXERCISE 3.1


CBSE Solutions for Class 10 Mathematics Pair of linear equations in two variable


Chapters in CBSE - Class 10 Mathematics


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