There r ten spots in library and each spot has 4 tables and ten readers ar there . 10 student come into liberary and want 2 study in how many ways that they sit in d liberary so that no chair would be blank?

There are no ways in which the students could sit to leave no chairs empty; the answer to your question is zero.

If there were ten spots in a library, and each spot consisted of four tables (we can presume there is one chair per table) that would mean 40 people would be able to sit in the library at one time. If there are already ten readers in the library and ten students enter to join them, that would make 20 people in the library in total. As there are 40 places in total, if each person was to sit down there would still be 20 chairs left empty. So there is no way in which this combination of people could sit to fill all of the chairs.

• How to solve logic problems involving mathematics

There are a number of ways in which you can go about solving a mathematical problem. Firstly, you should try to draw some sort of sketch to illustrate the problem. This shows the problem in a different way, encouraging your brain to approach it from another angle, which is useful if you are finding the problem challenging. If you still can't see how to figure out the answer, you should again try to look at the logic problem from another point of view.

Most logic problems don't require a high level of mathematics ability to be solved; they simply need an altered way of thinking. However, adapting your problem into an algebraic format could be helpful. Alternatively, look at similar logic problems to see how they have been solved. Solving logic problems can help develop your mental ability by encouraging you to follow a range of differing thought processes.