四十 (sìshí): forty; 40

Meanings

Tā jīnnián sìshí suì le.

He is forty years old this year.

Zhè běn shū yǒu sìshí yè.

This book has forty pages.

mistakes

四 (sì, 4th tone) and 十 (shí, 2nd tone) can be tricky together. Be careful not to confuse 四十 (40) with 十四 (14).

四 sì

十 shí