The cost of 2 pens and 2 books is LE. If the number of pens increases by 2 and the number of books decreases by 1, the cost becomes LE. Find the cost of one pen and that of one book.
Denote the cost of one pen by and the cost of one book by .
If the cost of 2 pens and 2 books is , then
The cost of 4 pens and 1 book is , so
The second equation can be arranged to give
Substituting this expression for into the first equation gives
an equation which can be solved for .
Finally, substitute this value of back into the equation for
Therefore, the cost of one book is and the cost
of one pen is .