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divide by 2! and 2! because there are 2 b`s and 2 `s. for example probabilty with the first b in 4th position and the second b in 6th position is 1 way and when you change the b`s you get a second way, but it is the same word. so you divide 2.
If your mind can conceive it and your heart can believe it, have faith that you can achieve it.
the number 2) was not so easy, but I got 4!/11! and 1/48^6
rc1979, christoph explained it well, there are 2 letters B (le'ts call it B1 and B2 for example)
Usually you have to work with permutation concerning words problems because order normally matters, in that case there will be no difference if you choose B1 or B2, it will be the same word whereas each B is considered as a specific letter. So you'll have twice more chances with B and it's the same idea for I.
finally, normally for a word with 11 different litters the prob will be 1/11! but since you have 2 repetitions of 2 letters, it will be 1*2*2/11!