It's a probability problem to find the odds of picking a green or red
shirt out of the 10 shirts on Thursday, Friday and Saturday since you
have randomly already know you have picked a blue shirt on the other
days. Not sure if you have this as a multiple question problem as you didn't list any possible answers (A. 7/20, B. 5/47, C. 2/5, D. 4/125) to the question. A, B, C, D being like 7 chances out of 20, 5 chances out 47, 2 chances out of chances 5 or 4 chances out of 125 (example answers only).
Probability = Number favorable outcomes / total number of outcomes
If you're asking for the probability of drawing said shirt colors on said days: Assuming there's no replacement (because clothes), the answer would be: (2/5)•(1/3)•(1/4), which equals 2/60, or 1/30. The reason: On Monday, there are 10 shirts, 4 of them blue. So, your chances are 4 out of 10, or 4/10, which reduces to 2/5. On Tuesday, there are 9 shirts left, 3 of them blue. So, 3/9, or 1/3. On Wednesday, there are 8 shirts, 2 of them blue. So, 2/8, or 1/4. You multiply all the fractions together (which is why simplifying helps A TON) Hope this helps! And sorry about not answering sooner!
The number of shelves must be a factor of the number of books from each category. (Because you are using multiple shelves). You are looking for the greatest amount, so you need to greatest, common factor (GCF) from each bunch of books.
