Solve probability problems.
We have 10 balls, which we label with numbers from 1 to 10 (different balls get different labels). Put all the balls in a bag and mix them. 2 balls are then randomly drawn from the bag.
Calculate the probability 
that the sum of the numbers on the drawn balls is 6.
Calculate the probability 
that the sum of the numbers on the drawn balls is at least 6.
Calculate the probability 
that the sum of the numbers on the drawn balls is equal to 6, if the
drawn balls are even numbers.
Calculate the probability 
that the sum of the numbers on the drawn balls is the smallest possible.
We have k balls, which we label sequentially with numbers from 1 to k (different balls receive different labels). Put all the balls in a bag and mix them. 2 balls are then randomly drawn from the bag. The probability 
that the sum of the numbers on the drawn balls is the smallest possible is 0.1. Calculate the number of all balls k.
