4. (3 points) A watercolor pen costs 1 yuan and 7 jiao. With 15 yuan, the maximum number of such watercolor pens that can be bought is $\qquad$.

将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。 

Note: The last sentence is a repetition of the instruction and should not be included in the translation. Here is the final translation:

4. (3 points) A watercolor pen costs 1 yuan and 7 jiao. With 15 yuan, the maximum number of such watercolor pens that can be bought is $\qquad$.
4. (3 points) A watercolor pen costs 1 yuan 7 jiao, with 15 yuan, you can buy at most $\qquad$ 8 such watercolor pens.

【Analysis】1 yuan 7 jiao $=1.7$ jiao, to find out how many such watercolor pens can be bought with 15 yuan, it is to find how many 1.7s are in 15, which can be solved by division.

【Solution】Solution: 1 yuan 7 jiao $=1.7$ jiao
$$
15 \div 1.7 \approx 8 \text { (pens) }
$$

Answer: With 15 yuan, you can buy at most 8 such watercolor pens.
Therefore, the answer is: 8.
【Comment】This problem examines the application of division with a remainder, note that the result should be rounded down using the "truncation method".