EXAM P SAMPLE SOLUTIONS
EXAM P SAMPLE SOLUTIONS
EXAM P SAMPLE SOLUTIONS
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14. Solution: A<br />
1 11 1 1 1 ⎛1⎞ p k = pk−1 = pk−2 = ⋅ ⋅ pk−3 = ... = ⎜ ⎟ p0 k ≥ 0<br />
5 55 5 5 5 ⎝5⎠ k<br />
∞<br />
1 = ∑ pk k= 0<br />
p 0 = 4/5 .<br />
∞<br />
⎛1⎞ = ∑⎜<br />
⎟<br />
k=<br />
0⎝5⎠<br />
p0<br />
p0 =<br />
1<br />
1− 5<br />
5<br />
= p0<br />
4<br />
Therefore, P[N > 1] = 1 – P[N ≤1] = 1 – (4/5 + 4/5 ⋅ 1/5) = 1 – 24/25 = 1/25 = 0.04 .<br />
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15. Solution: C<br />
A Venn diagram for this situation looks like:<br />
We want to find<br />
( )<br />
w= 1−<br />
x+ y+z<br />
1 1<br />
We have x+ y = , x+ z = , y+ z =<br />
4 3<br />
5<br />
12<br />
Adding these three equations gives<br />
1 1 5<br />
( x+ y) + ( x+ z) + ( y+ z)<br />
= + +<br />
4 3 12<br />
2 x+ y+ z = 1<br />
( )<br />
1<br />
x+ y+ z =<br />
2<br />
1 1<br />
w= 1− ( x+ y+ z)<br />
= 1− =<br />
2 2<br />
Alternatively the three equations can be solved to give x = 1/12, y = 1/6, z =1/4<br />
⎛ 1 1 1⎞ 1<br />
again leading to w = 1−<br />
⎜ + + ⎟=<br />
⎝12 6 4 ⎠ 2<br />
k<br />
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