The cost of a chocolate is Rs (x + y) and Rohit bought (x + y) chocolates. Find the total amount paid by him in terms of x. If x = 10, find the amount paid by him.

Solution:

Given, cost of a chocolate = Rs (x + y),

Rohit bought (x + y) chocolates

∴ The total amount paid by him in terms of x = cost × number of chocolates bought

= (x + y) (x + y)

= (x + y)²

Using standard identity : (a + b)² = a² + 2ab + b²

= x² + y² + 2xy

Also given that, if x = 10, find the amount paid by him.

Now, we have

The total amount paid = x² + y² + 2xy

= (10)² + y² + 2(10)y

= 100 + y² + 20y

✦ Try This: The cost of a pen is Rs (2x + y) and Ratan bought (x + 3y) pens. Find the total amount paid by him in terms of x. If x = 15, find the amount paid by him.

Given, cost of a pen = Rs (2x + y),

Ratan bought (x + 3y) pens

∴ The total amount paid by him in terms of x = cost × number of pens bought

= (2x + y) (x + 3y)

= 2x² + 6xy + xy + 3y²

= 2x² + 7xy + 3y²

Also given that, if x = 15, find the amount paid by him.

Now, we have

The total amount paid = 2x² + 7xy + 3y²

= 2(15)² + 7(15)y + 3y²

= 450 + 105y + 3y²

☛ Also Check: NCERT Solutions for Class 8 Maths Chapter 9

NCERT Exemplar Class 8 Maths Chapter 7 Problem 105

The cost of a chocolate is Rs (x + y) and Rohit bought (x + y) chocolates. Find the total amount paid by him in terms of x. If x = 10, find the amount paid by him.

Summary:

The cost of a chocolate is Rs (x + y) and Rohit bought (x + y) chocolates. The total amount paid by him in terms of x is x² + y² + 2xy. If x = 10, the amount paid by him is Rs.100 + y² + 20y

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