Uniform continuity – The probability of the nth event is between x and y

I have an even distribution of age in the range $$[Ab)[Ab)[ab)[ab)$$ with $$a = 42$$ and $$b = 78$$

So, the probability that a person walks in a bank located between $$50$$ and $$70$$ years would be $$frac {70-50} {78-42}$$, right?

But I'm struggling with this problem where I'm supposed to find

1. The probability that 3 out of 7 customers in the bank are between $$50$$ and $$70$$ years of age
2. The probability that the $$7$$ customer entering the bank is between $$50$$ and $$70$$ years of age
3. The probability that the $$7$$ customer entering the bank is also the 3rd customer between $$50$$ and $$70$$ years of age

For $$1.$$is it right $$frac {20} { binom {7} {3}}$$?

And for $$2.$$ and $$3.$$I am a little lost so I need help on them