Question

Seven pens and two pencils costs $6.59. seven pens and five cost $7.55. Find the cost of one pencil and the cost of one pen.

Answer 1

Let one pen be $x$ and one pencil as $y$, we can produce two equations in terms of $x$ and $y$

$7x+2y=6.59$ ------> Equation 1
$7x+5y=7.55$ ------> Equation 2

We can use either Elimination or Substitution method. Let's try the substitution method

Rearranging equation one to get $7x=6.59-2y$ and substitute into equation 2, gives
$(6.59-2y)+5y=7.55$
$6.59+3y=7.55$
$3y=7.55-6.59$
$3y=0.96$
$y=0.32$

We can use either equation one or equation to work out $x$

$7x+2(0.32)=6.59$
$7x=6.59-0.64$
$x=0.85$

The price of one pen is $0.85
The price of one pencil is $0.32