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random from the set

by sanju09 » Fri Jul 23, 2010 3:01 am
n is an integer chosen at random from the set

{5, 7, 9, 11}

p is an integer chosen at random from the set

{2, 6, 10, 14, 18}

What is the probability that n + p = 23?
A. 0.1
B. 0.2
C. 0.25
D. 0.3
E. 0.4

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by selango » Fri Jul 23, 2010 3:04 am
n+p=23

5+18=23

9+14=23

1/4*1/5=1/20

1/20+1/20=1/10=0.1

Pick A
Last edited by selango on Fri Jul 23, 2010 9:33 am, edited 1 time in total.
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by kvcpk » Fri Jul 23, 2010 3:22 am
n is an integer chosen at random from the set

{5, 7, 9, 11}

p is an integer chosen at random from the set

{2, 6, 10, 14, 18}

n+p should be 23.
5+18 makes 23.
Probability is
1/4 * 1/5 = 1/20

9+14 makes 23
probability is
1/4*1/5 = 1/20

One of these should happen. Hence 1/20 +1/20 = 1/10 =0.1
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