Answer:
50 black keys
Step-by-step explanation:
for every set of 7 white keys there are 5 black keys
72/7 = 10
so there is a total of 10 full sets of keys
then you have 2 white keys remaining but that doesn't matter because they will just be on the dies and already have a black key next
so this means that you only have to calculate the number of 10 sets of black keys and thats 5 x 10.
hope this helps : )
