Answer:

(4) 1:2

Step-by-step explanation:

Amit's present age given 20 so 5 years ago he would be 15 and 5 years ago his mother was thrice of his age. ie.,

amit age = 15

mother's age = 15×3 = 45

so,

amit present age = 20

mother's present age = 45+5 = 50

now, 10 years from now the ratio of their ages

amit's age = 20+10 = 30

mother's age = 50 + 10 = 60

thus, 30:60 = 1:2