Question:
The cost of 4 pens and 4 pencils boxes is 1100. Three times the cost of a pen is ₹ 15 more than the cost of a pencil box. Form the pair of linear
equations for the above situation. Find the cost of a pen and a pencil box.
Solution:
Let the cost of a pen be ₹ x and the cost of a pencil box be ₹ y.
Then, by given condition,
$4 x+4 y=100 \Rightarrow x+y=25$ $\ldots($ (1)
and $\quad 3 x=y+15$
$\Rightarrow \quad 3 x-y=15 \quad$...(ii)
On adding Eqs. (i) and (ii), we get
$4 x=40$
$\Rightarrow \quad x=10$
By. substituting $x=10$, in Eq. (i) we get
$y=25-10=15$
Hence, the cost of a pen and a pencil box are ₹ 10 and ₹ 15, respectively.