Quadratic Equations | Exercise 4.2

Question 6

A cottage industry produces a certain number of pottery articles in a day. It was observed on a particular day that the cost of production of each article (in rupees) was 3 more than twice the number of articles produced on that day. If the total cost of production on that day was ₹ 90, find the number of articles produced and the cost of each article.

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Solution

We will form a quadratic equation from the given information and solve it.

Step 1 — Set up the equation

Let's define the number of articles.

Let the number of articles be xx.

Now, let's define the cost of each article.

The cost of each article is 2x+32x + 3 rupees.

The total cost is the number of articles multiplied by the cost of each.

The total cost is given as ₹90.

So, we can write the equation.

x(2x+3)=90x(2x + 3) = 90

Let's expand this equation.

2x2+3x=902x^2 + 3x = 90

We need to bring all terms to one side.

2x2+3x90=02x^2 + 3x - 90 = 0

2x2+3x90=0\boxed{2x^2 + 3x - 90 = 0}

Diagram 1

Step 2 — Solve for the number of articles

We have a quadratic equation.

Let's solve it by splitting the middle term.

We need two numbers that multiply to 2×(90)=1802 \times (-90) = -180.

These numbers must also add to 3.

The numbers are 15 and -12.

So, we can rewrite the middle term.

2x2+15x12x90=02x^2 + 15x - 12x - 90 = 0

Now, let's factor by grouping.

x(2x+15)6(2x+15)=0x(2x + 15) - 6(2x + 15) = 0

We can factor out the common term (2x+15)(2x + 15).

(2x+15)(x6)=0(2x + 15)(x - 6) = 0

For the product to be zero, one of the factors must be zero.

So, either 2x+15=02x + 15 = 0 or x6=0x - 6 = 0.

2x+15=0    2x=15    x=1522x + 15 = 0 \implies 2x = -15 \implies x = -\frac{15}{2}

x6=0    x=6x - 6 = 0 \implies x = 6

The number of articles cannot be negative.

So, we reject x=152x = -\frac{15}{2}.

Therefore, the number of articles is 6.

Number of articles=6\boxed{\text{Number of articles} = 6}

Step 3 — Calculate the cost of each article

We found the number of articles, x=6x = 6.

The cost of each article is 2x+32x + 3.

Let's substitute the value of xx.

Cost=2(6)+3\text{Cost} = 2(6) + 3

=12+3= 12 + 3

=15= 15

So, the cost of each article is ₹15.

Cost of each article=15\boxed{\text{Cost of each article} = ₹15}

Answer

(i) The number of articles produced is 6. (ii) The cost of each article is ₹15.

More questions in Exercise 4.2

Q1

Find the roots of the following quadratic equations by factorisation:

(i) x23x10=0x^2 - 3x - 10 = 0

(ii) 2x2+x6=02x^2 + x - 6 = 0

(iii) 2x2+7x+52=0\sqrt{2}x^2 + 7x + 5\sqrt{2} = 0

(iv) 2x2x+18=02x^2 - x + \frac{1}{8} = 0

(v) 100x220x+1=0100x^2 - 20x + 1 = 0

Q2

Solve the problems given in Example 1.

Q3

Find two numbers whose sum is 27 and product is 182.

Q4

Find two consecutive positive integers, sum of whose squares is 365.

Q5

The altitude of a right triangle is 7 cm less than its base. If the hypotenuse is 13 cm, find the other two sides.

Q6

A cottage industry produces a certain number of pottery articles in a day. It was observed on a particular day that the cost of production of each article (in rupees) was 3 more than twice the number of articles produced on that day. If the total cost of production on that day was ₹ 90, find the number of articles produced and the cost of each article.

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