This is a method using model. The easier way for students in
Primary school to understand. I hope my reply is not too late. I
really hope you would understand the model.
Firstly, since 8 is able to be divided by the 4 units, we wil do
exactly that. Since the units are equal for both the grey and black
marbles, we can also do the same for the units representing the
black marbles.
Secondly, we will now look at the black marbles. since we can
see that apart from the 5 original units, we still need 6 more
units, since there are 11 units altogether in the end, we can draw
6 more unit, the size of (an original unit-2). Now, you must wonder
where does this 6 units come from. Firstly, they come from the 20
marbles that are added in. But that is not all, there is also the
10 extra ones that we took out from the original unit. Thus, we can
say that the 6 units is equals to 20+10. From there, i'm sure that
you can work out the answer yourself.
My answer is: Blue-20marbles, Black-55 marbles.
I hope my answer is correct and i hope that it has helped you!
This method can be used if any of the before and after ratio is the
same; like this question.
