Question

a shopkeeper buys a certain amount of books for rs.720.if the cost per book was 5 less , the no.of books that could be bought for rs720 would be 2 more. taking the original cost of each book to be rs.x , write an equation in x and solve it

Answer 1

the equation in x is x2-5x-720=0

Answer 2

Answer:

Let the original price of 1 book be x

No. of books brought by Rs.x = 1

No. of books brought by Rs.720 = $\frac{720}{x}$

Now the original price is decreased by Rs.5

So, new price of 1 book = x-5

No. of books brought by Rs.720 = $\frac{720}{x-5}$

We are given that if the cost per book was 5 less , the no.of books that could be bought for Rs 20 would be 2 more.

So,  $\frac{720}{x-5}-\frac{720}{x}=2$

$\frac{720x-720x+3600}{x^2-5x}=2$

$\frac{1800}{x^2-5x}=1$

$x^2-5x-1800=0$

$x^2-45x+40x-1800=0$

$x(x-45)+40(x-45)=0$

$(x+40)(x-45)=0$

$x = -40,45$

Since Price cannot be negative

So, the original price of 1 book is Rs.45