Question

If $7$ pens and $3$ books cost $Rs1395$, while $5$ pens and $4$ books cost $Rs1665$. Find the cost of a book

• A. $360$
• B. $45360$
• C. $35350$
• D. $noneofthese$

Answer 1

The correct option is A $360$

Let the cost of $1$ pen be $x$

and the cost of $1$ book be $y$

Then $7x+3y=1395$-----$\left(1\right)\times 4$

$5x+4y=1665--\left(2\right)\times 3$

$4\times \left(1\right)$ -------- $3\times \left(2\right)$

$(28x+12y)-(15x+12y)=5580-4995$

$13x=585$

$x=45$

Putting $x=45$ in (1)

$7\times 45+3y=1395$

$\Rightarrow 315+3y=1395$

$\Rightarrow 3y=1395-315$

$\Rightarrow 3y=1080$

$\Rightarrow y=360$

Therefore Cost of one pen is Rs $45$ and cost of one book is Rs $360$