Abox was 3/4 full of marbles. the box fell on the floor. thirty marbles fell out. this was 20% of the marbles in the box. how many marbles would a full box contain?

What is the approximate circumference of the circle shown below?

Ascientist wants to use a model to present the results of his detailed scientific investigation. why would a model be useful? a )because the model makes the concepts easier to understand b) because the model is easy to put together and to use c) because the model prevents other scientists from asking questions d) because the model requires the audience to pay full attention to it i don't know what to choose because between a and d a is much more likely than d because it only wants to get the attention of the audience. i'm confuse.

Ithink i know it but i want to be sure so can you me out ?