How do I work out this statistical problem ?

do you get chips when a certian number is picked?
do you get the number of chips picked by the RNG?

For a question like this, you need to be specific.

Oh sorry yes I was suppose to say you get chips when 1 or 9 is chosen

On any day there is a 2/10 = 1/5 chance of getting chips. The chances of getting chips exactly twice in the 15 days in three weeks is therefore C(15,2)(1/5)^2(4/5)^13, where C(15,2) is the number of combinations of 2 in 15 and equals 15*14/2.