Let us suppose that the number of grapes in the box is x and the number of grapes in the basket is y.
It means that the weight of the grapes in the box is x kg and that of basket is y kg.
It has been given that the box had twice as many grapes as a basket. Therefore, we have
Now when we add 2 kg to the basket then the weight of the basket is y+2 and the weight of box will remain same.
Now, we have been given that after 2 kilograms were added to the basket it contained 0.5 kilograms more than the box. Hence, we have
Substituting the value x=2y in the equation, we get
Therefore, the basket contains 1.5 kilograms of grapes.