A rain drop randomly drops on the keys of a piano, what is the probability that the drop landed on a black key? (Assume that the drop had to land on a key and did not land on two at the same time).

Carli has 90 apps on her phone. braylen has half the amount of apps as theiss. if carli has three timesthe amount of apps as theiss, how many apps does braylen have? let b represent the number of braylen's apps and t represent the number of theiss's apps.