一万三 is a colloquial abbreviation for 一万三千 (13,000). In Chinese, when a number ends with a digit after 万 (ten thousand), the final digit is often dropped in casual speech, especially in prices or quantities. This pattern is common: 一万五 (15,000), 两万八 (28,000). The pinyin given (yī mò) reflects a non-standard reading — the standard pinyin for 一万三 is yī wàn sān. This usage is informal and most frequent in spoken contexts like bargaining or quoting prices.