Question

The cost of 12 books is Rs. 450. Find the cost of 7 books.

Answer 1

Hint: We have the cost of 12 books. We can find the cost of 1 book from it by dividing the cost of 12 books by the 12. Then we can find the cost of 7 books by multiplying the cost of 1 book with the number of books which is 7.

Complete step by step Answer:

Let us assume x is the price of one book.
We are given that 12 books cost Rs. 450. Then we can write it in terms of x.
$ \Rightarrow 12x = 450$
The cost of 1 book is given by dividing the cost of 12 books by the 12.
$ \Rightarrow x = \dfrac{{450}}{{12}}$
After doing the division, we get,
\[ \Rightarrow x = 37.5\]
Therefore, the cost of 1 book is Rs. 37.5
Now we have the cost of 1 book. To find the cost of 7 books, we need to multiply 7 with the cost of one
book.
Let, y be the cost of 7 books. So, we can write,
$y = 7 \times x$
On substituting the values of x, we get,
$ \Rightarrow y = 7 \times 37.5$
$ \Rightarrow y = 262.5$
Therefore, the cost of 7 books is Rs. 262.5.

Note: Alternate approach to this problem is by the concept of proportionality.
Let x be the cost of 7 books.
We are given that the cost of 12 books is Rs. 450.
Using proportionality, we can write,
$\dfrac{x}{7} = \dfrac{{450}}{{12}}$
On cross multiplying, we get,
\[ \Rightarrow \]$12x = 450 \times 7$
Dividing throughout with 12, we get,
$ \Rightarrow x = \dfrac{{450 \times 7}}{{12}}$
After doing the calculation, we get,
$ \Rightarrow x = 262.5$
Therefore, the cost of 7 books is Rs. 262.5.