Answer:
286
Step-by-step explanation:
First, we can tell that this is either a combination or permutation because we have to determine the number of possible combinations based on a limited number of options and a set number of pieces to practice each day.
Next, because order doesn't matter (it doesn't matter if she practices P1 or P3 first, for example), this is a combination.
After that, we can repeat a piano piece, so there is repetition
If there are n things to choose from, and we have to choose r things, our formula for a combination with repetition is
(r+n-1)!/(r!(n-1)!)
Here, we choose from 4 pieces and we need to choose 10 each day, so we have
(r+n-1)!/(r!(n-1)!) = (4+10-1)!/(10!(4-1)!) = 13!/(10!3!) = 13*12*11/(3*2*1) = 286 possible combinations
