Question
In a single cast with two dice the odds against drawing $$7$$ is :
A.
$$\frac{1}{6}$$
B.
$$\frac{1}{{12}}$$
C.
$$5:1$$
D.
$$1:5$$
Answer :
$$5:1$$
Solution :
$$E = \left\{ {\left( {1,\,6} \right),\,\left( {2,\,5} \right),\,\left( {3,\,4} \right),\,\left( {4,\,3} \right),\,\,\left( {5,\,2} \right)\left( {6,\,1} \right)} \right\}$$
$$\therefore \,P\left( E \right) = \frac{6}{{6 \times 6}} = \frac{1}{6}.$$ So, the odds against drawing $$7 = \frac{{P\left( {\overline E } \right)}}{{P\left( E \right)}} = \frac{{1 - \frac{1}{6}}}{{\frac{1}{6}}} = \frac{5}{1}.$$