Question

David is six years old. His sister is half his age. So when David is 100 what is her sister age.

Answer 1

David's sister age is 50

Answer 2

david is six years old
then his sister =1/2*David age
=1/2*6
=3
when David is 100 year
his sister will be 100/2
=50 year old
$1 \div 2 \times 100 \\ = 50$