self Maths Puzzle

Marina is taking chemistry, math, and physics classes at school. She has two books for chemistry, three for math, and one for physics. How many ways can Marina arrange her books on the shelf if she wants the books for each class to be next to each other?

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self Other Question

The sequence S is defined by S1=1 and Sn=Sn−1+n for n≥2. What is S36?

Consider a 16×16 chessboard. How many unordered pairs of distinct 1×1 squares are there on the chessboard which have at least one corner in common?
Details and assumptions

A pair of squares have at least one corner in common, if there is a point which lies on both squares.