A die is weighted so that the probability of its landing faceuppermost isi/21. This die is thrown and ifishows uppermost,ifair dice are throwni

(A total score is obtained by summing the numbers showing uppermost on thesei = 1,2,3,4,5,6).fair dice.

1) Find the probability that the total score is 4

2) Find the probability that 2 fair dice were thrown, given that the total score is 4.

At the first attempt of this question, I got there are 4 ways which you can a total score of 4 when you rolldice.i

When throwing: 1 die gives only one choice, that is number 4

2 dice give (1,3),(2,2),(3,1) which the sum is 4

3 dice give (1,1,2),(1,2,1),(2,1,1) which the sum is 4

4 dice give (1,1,1,1)

Cuz I am not allowed to use tree diagram, so I have to use the formulae of probability

I've just done up to here then I got stuck, I think somehow we have to usethe law of total probability.

Can some body help me to do part 1 and give hints on part 2 please?

Thank you very very much for your time.