Because they exchanged a piece of writing paper, and then they had it.

4 notebooks+1 pen = 1 notebook +3 pens

Then we can know: 3 notebooks =2 pens.

Then the price ratio of notebook and pen is 2: 3.

It took 22 yuan five books and four pens.

2×5+4×3=22

22÷22= 1 yuan

Then the price of a pen is 1×3=3 yuan.

The price of a notebook is 1×2=2 yuan.