suppose that 2 balanced dice are tossed repeatedly and the sum of the 2 uppermost faces is determined on each toss. what is the porbabilty that we obtain a sum of 3 before we obtain a sum of 7.

my working:

since obtain 3 and 7 are independent,

P( getting sum of 3) = 2/6 x 1/6

P ( getings sum of 7) = 3/6 x 1/6

so the answer should be 2/6 x 1/6 x 2/6 x 1/6

but my book says taht it is 1/4...