มีกี่ประเทศที่พูดทั้งภาษาอังกฤษและภาษาดัตช์?
How many countries speak both English and Dutch?
country = pd.DataFrame(columns=['Name', 'Code']); countrylanguage = pd.DataFrame(columns=['CountryCode', 'Language'])
country[country['Code'].isin(countrylanguage[countrylanguage['Language'] == 'English']['CountryCode']) & country['Code'].isin(countrylanguage[countrylanguage['Language'] == 'Dutch']['CountryCode'])]['Name'].nunique()