Question

$5$ books and $7$ pens together cost Rs. $79$ whereas $7$ books and $5$ pens together cost Rs. $77$. Find the total cost of $1$ book and $2$ pens.

Answer 1

Let the cost of 1 book =$x$

And the cost of 1 pen =$y$

$\Rightarrow 5x+7y=79$

$\Rightarrow 7x+5y=77$

Equation (1) × 7 : $35x+49y=79\times 7$

Equation (2) × 5 : $35x+25y=77\times 5$

Subtract two equations ;

$\Rightarrow 24y=168$

$\Rightarrow y=7$

$\Rightarrow x=6$

Total cost of 1 book and 2 pens $=x+2y=6+14=20$