The life span of a horse is half that of a tiger, that is, half that of a tiger, that is, (1+ 1/2) times, so the life span of a horse is 30 years. Ma said that the life span of a lion is one third longer than that of a lion, and 40 is indeed longer than 30 1/3, which further proves the correctness.
Writing in mathematical language is:
The life span of tiger, lion and horse is set as A, B and C respectively, so A=20, A=( 1- 1/2)B, so B = 40.
C=( 1+ 1/2)A=30, or B=( 1+ 1/3)C, then C=30.